I’m so sorry that it’s taken me this long to get to your question. I didn’t have access to a computer for awhile and I absolutely hate writing long posts (meta in particular) on mobile, so I was waiting until I had my computer again to respond.

That aside, let’s dive in! I’m going to try my best to create a timeline of significant events relating to Bellamy’s feelings, but I find Bellamy to be a bit trickier than Clarke for some of these things (like when he started trusting her) so I’m sure other people’s opinions will differ. Also keep in mind that there’s no way I could hit every Bellarke moment (even though I wish I could) so I’m just hitting the main milestones in the evolution of Bellamy’s feelings for Clarke.

1) 1x03

Originally posted by insertacoolurl

Bellamy, to me, started respecting Clarke after she mercy-killed Atom. Before this moment, he thought that she was just a prissy privileged girl from the Ark who was here to continue doing the council’s bidding - as always. He didn’t think she really cared about the kids, just how them being alive might benefit her.

At the beginning of the episode Bellamy tells Clarke that she doesn’t have the guts to make the hard choices. She proves him wrong by killing Atom even when Bellamy couldn’t. And she also proves him wrong that she doesn’t care about the kids on the ground because by releasing Atom from his pain, at her own expense, she proves that she does. This is the moment I believe Bellamy starts to respect Clarke. That’s why the camera lingers on his reaction and why he looks at her like that. I don’t think it’s supposed to be a romantic moment (although it’s possible that this is one of those little hints that something COULD happen in the future from the writers), but it is still a significant moment in their relationship. It is to show that something has changed.

Bellamy demonstrates his new respect for her by telling the delinquents to get Clarke whatever she needs at the end of the episode. He now trusts her judgement (not necessarily trusts her completely yet, as Bellamy must have trust issues after his time on the Ark).

2) 1x04

“For now, we make the rules.”

Bellamy begins to look at Clarke as an ally, not an adversary, at the end of 1x04 after the whole Charlotte/Murphy debacle. At the beginning of the episode, they had differing views on how to handle the (fake) knowledge that Murphy was responsible for Wells’ murder. By the end of the episode, it showed that ignoring each other (Clarke ignored Bellamy about not telling the rest of the delinquents/Bellamy ignored Clarke about not hanging Murphy) proved to be destructive. They also realized that in order for things to work out, they need to work with each other, not against each other. And, they also can’t lead on their own - they need each other to balance each other out (the whole head and heart thing, right?). At the end of the day, they have the same objective - keep the kids alive. Bellamy (and Clarke) realized this in this moment, and they have been leading together ever since (the DELINQUENTS, that is - it gets a bit tricky when you look at the Sky People as a whole).

3) 1x03 - 1x08

Look, I have no idea when Bellamy started to trust Clarke. I cannot pinpoint the moment when it happened, just like I cannot pinpoint the moment that they fell in love either - and I think there’s a reason for that. I don’t think, with Bellamy, there was a moment where he started trusting her. To be clear, Bellamy did start trusting Clarke, but it wasn’t a specific thing or moment in time that made him do it. I do believe, though, that it a variety of smaller moments between the episodes of 1x03 and 1x08 that made him start trusting her, and ALL of them are important, not just one of them.

One such moment was the Atom/mercy-killing scene, because in that moment she lifted a burden from his shoulders that she didn’t have to, and he learned that she had the delinquent’s best interests at heart, not just the Ark’s. Another was the scene where she told him that they make the rules - not just her: both of them. And then there was Clarke telling him in 1x05 that he always did what he had to do to protect his sister, and that’s who he is. Why that scene? Because she proved that she knows who he really is and can see the best in him, even when he, himself, can’t. Then, again, when Clarke helped him look for Octavia in 1x06, that was another moment that made him trust her just a little bit more.

There were other moments, too, to be certain. All I know is that by the time 1x08 came to a close, he trusted Clarke completely. “Day Trip” was the episode that solidified the trust.

When Clarke went after Dax when he was beating up Bellamy, despite being practically unarmed and at a disadvantage except for a gun she didn’t know how to shoot, she proved that she would risk her life for him. In the tree scene, she proved that she would support him. And, in the radio scene, Clarke proved that she would have his back, no matter what. When you add that to all the prior scenes, you get complete trust. But it didn’t happen in one scene or one instant - it happened over time. The trust was strengthened, but it didn’t materialise randomly one day.

(Interestingly, this is also the episode Clarke told Finn she trusted Bellamy - whether it’s when she initially started trusting him or not. Doesn’t have a lot to do with Bellamy’s own feelings, but an interesting connection all the same.)

4) 1x08

I think that even from the moment they met, Bellamy probably though “yeah, I guess she’s cute but she’s annoying as hell” and didn’t dwell on her appearance, because he just didn’t care that much. That’s how it usually is. But this moment in “Day Trip”, when he gets flustered teaching Clarke how to shoot, is the first acknowledgement that there might be some aesthetic attraction going on now, where there wasn’t before. It’s not the first time he’s noticing that Clarke is attractive - but it’s the first time he’s been hyper-aware of it, and it’s gotten him all messed up. (Which is funny, coming from the guy sleeping around camp with his cocky facade.) So there’s the aesthetic attraction, which I believe Bellamy is aware of, but I don’t think he’s aware of any other kind of attraction at this point.

5) 1x08

Yep, more “Day Trip”. There’s a lot going on in this episode - what can I say?

This is also when Bellamy starting looking at Clarke as more than just a partner, but a friend too. I believe that before this they were already growing towards a friendship, but this episode - specifically the tree scene - just served to establish it quicker than if it hadn’t happened at all. We can see by the lighthearted flirting in the next episode that the bad blood between them is gone - they’re friends now (on the path to something more, in my opinion).

I think that this tree scene is a large part in why Clarke is so special to him. Think about it: Bellamy hasn’t really had a real friend before. In order to protect Octavia, I’m sure he had to isolate himself on the Ark, so no one ever got close enough to him to find out what he was hiding. Bellamy wouldn’t take a chance like that. And even if he did have a friend, they would never scratch the surface because he would never be able to fully trust them or tell them things like he can with Clarke. That’s only one of the reasons the beginning of Bellarke is so beautiful.

6)  2x05

I’ve gone over all the major milestones for Season 1 (even though I didn’t talk about one of my personal favourites, “I Am Become Death” *cry*). Now it’s on to Season 2, and this is where Bellamy’s feelings start escalating.

I am of the opinion that Season 1 Bellarke wasn’t about romance. It was about partnership, friendship, and establishing the base of their bond before building upon it. I don’t think the writers knew for certain that they were going to go in the romance direction, but they were considering it (hence the flirting and Bellamy getting flustered) so they were keeping their options open. I think they decided it was going to be a slow burn romance when they were writing Season 2 - this became obvious to me in 2x05.

I could talk about the amazing hug scene, but since I’m looking for more distinct moments where Bellamy’s feelings are shown more clearly (not that the hug wasn’t clear, but I think the campfire makes it even clearer) I’m going to talk about the campfire scene.

This is the scene where I think it becomes clear that Bellamy is developing feelings for Clarke (maybe not fully in love with her yet, but he’s definitely getting there). The scene deliberately shows Bellamy looking at Octavia and glancing at Clarke, seeming sort of confused. Why? Because he feels differently about them. With his sister, it’s familial love. With Clarke, it used to be like that, but something’s changed and he doesn’t understand what it is. He’s never felt this way before. So while I think this is when Bellamy develops his feelings for Clarke, I don’t think he knows what those are, exactly, and it confuses the hell out of him. I don’t know if you guys have noticed (I mean, we over-analyse everything so I’m sure you have) but the mood between Clarke and Bellamy in Season 2 is very different from Season 1 - there’s a reason for that.

7) 2x09

So Bellamy’s feelings are established at this point (not stated explicitly, but you can gather it). This is the episode that it is clear to Bellamy (and the audience) that he would do anything for Clarke - sacrifice himself for her without hesitation. I, personally, believe that that that’s been true since Season 1, even, but this is the episode it’s made obvious.

First, we get the fabulous Bellamy-being-a-dramatic-hoe-and-knocking-the-supposedly-poisoned-cup-out-of-Clarke’s-hand-and-then-proceeding-to-step-in-front-of-her-to-protect-her scene, which is incredible and then Bellamy goes on to say what we’ve already figured out at this point at the end of the episode: that he would do anything for her.

“He’d do anything for her - to protect her. It just makes sense.”

And, yes, that is confirmed to be about Clarke by one of the writers, thank you very much.

8) 2x05 - 2x16

I don’t know when it happened, okay? - but no one can convince me that Bellamy Blake is not completely infatuated with Clarke Griffin when she leaves him crying outside the gates of Camp Jaha in the Season 2 finale. Like I said, I can pinpoint Bellamy falling in love with Clarke no better than I can pinpoint when Bellamy started trusting her. It didn’t happen in a second, it wasn’t love at first sight, it just was. And at some point it became right. I don’t know when that was. Realistically, it was probably a lot of smaller moments that resulted in this: Bellamy falling in love. It started with the feelings he had in 2x05, and those feelings just grew bigger and stronger over the course of the season, just as they continue to grow bigger and stronger even though we’re moving onto Season 4 now. Regardless, by the time Season 2 is over, Bellamy is in love (I still don’t think he realizes this, though) - that is very clear to me.

9) 3x02

This is the moment that Bellamy realizes he cannot lose Clarke. To be clear, it’s not like he necessarily thought he could before, but in this episode he is truly faced with what Clarke dying really means - and he can’t cope with that. He is the most off-kiltered and torn up by the thought of losing Clarke in this episode - he’s never been like this at any other point in the show. This is when Bellamy realizes the extent of what Clarke means to him. He can’t lose her. He just can’t.

10) 3x03

This was a painful moment for me, and a lot of Bellarkers. But why is that? Not a whole not happened, they barely said anything to each other. I think I know why this scene in particular was so painful. Look at Bellamy’s eyes. He stares at Clarke, searching her face, but he finds that he doesn’t recognize her anymore. And then he looks to L.exa, and he realizes why - he blames L.exa for making Clarke this way, into this unrecognizable girl. What happened to the girl who told him she needed him? Did she even mean that? He doesn’t think so.

This scene is so horribly painful because it is the scene where his trust in Clarke, so carefully built in Season 1 and 2, breaks. He can no longer trust this girl - this Wanheda. This is not the Clarke he fell in love with. This is a product of the Grounders and he can’t, for the life of him, understand when everything changed (because it happened when he was either in Mount Weather or in Arkadia, when Clarke wasn’t with him) and how Clarke could have possibly left him behind after everything.

11) 3x05

Obviously another important scene. This one, not to be confused with the one in 3x02, is the scene that it becomes obvious to the audience that Bellamy needs Clarke. But it’s more than just needing her to be alive, like in 3x02, he needs her with him. He needs her to be there, because he cannot be truly whole without her. That’s not to say he can’t function without her, but he’s his best person when she’s there (and the same goes for her). Bellamy, to this day, has never told Clarke he needs her, but he does.

I think that Bellamy, when he says the words “you left me” briefly comes to this conclusion that he needs Clarke, but under the current circumstances that’s not something he wants to be true (or can even afford to be true). The thought that he might actually need someone else, someone who has left him before (twice, if you count Polis) scares him shitless. So he ignores it and pushes it down somewhere deep inside him where he will not have to address it anymore (much like Clarke with her feelings for Bellamy in 2x09). And then he pretends the fact doesn’t exist, in a matter of seconds, and corrects himself: “you left everyone”. He makes it impersonal, even though the whole situation is far from impersonal. I think him getting angry with Clarke was a result of bottled up emotions he had towards her, but it was also about convincing himself that he doesn’t need her after all - that she isn’t worth it.

It doesn’t work.

11) 3x11 - 3x13

Two things happened over the course of these three episodes. The first - number eleven - is the rebuilding of trust. I believe that by the end of 3x13, Bellamy has started to trust Clarke again. I don’t think that, by the end of Season 3, he is quite at the point he was before Clarke left him, but he’s getting there, and I hope it’s something we get to see in Season 4.

The first thing Clarke does to get him to trust her again is returning to him, and proving once again that she does still care about the well-being of the delinquents by trying to help Raven. She also goes so far as to ask him if he’s okay, which is something no one else has actually bothered to do - despite everything Bellamy did in 3x05, she showed him that she still cared. Later, she provided more evidence of how much she cares by tending to his hand, just like he did for her. It was such a caring gesture, and probably an unnecessary one, but I think it was Clarke’s way of showing him that she still cares. Bellamy starts to trust her enough that he even opens up to her a bit, by asking her what you do when you realize you might not be the good guy anymore. Her response (”maybe there are no good guys”), equally comforting and not (if that makes sense), shows him that Clarke is still in there.

The trust between them builds more in 3x12 and then they reach a point close (but not quite) to where they used to be in 3x13. Clarke does what she did in “Day Trip” and shows Bellamy that she’s there for him, no matter what happens and the things he does, when she follows him onto that beach. Bellamy recognizes that and he recognizes her in a way he just couldn’t in 3x03. Clarke further shows that he matters to her by quoting him when they drink Luna’s vials and says the word “together”.

Trust is restored - mostly, anyway. Talk to me again in Season 4.

12) 3x11 - 3x13

The second thing these three episodes does is allow Bellamy time to forgive Clarke. It goes hand-in-hand with him learning to trust her again. I think that in 3x11, him bandaging her hand was in part him trying to heal what broke between them 3x03 and again in 3x05. It’s part apology, part forgiveness. I don’t think Bellamy has the heart to really stay angry with Clarke after all that he has done, himself, so he doesn’t get mad at her again.

The forgiveness isn’t complete, however, until he tells her that he doesn’t want to be angry with her anymore in 3x13. It’s such a mature decision for Bellamy to make and I, as a viewer, was so proud of him for doing it.

13) 3x14

Lots of people considered this episode to be a bit dry in terms of Bellarke, but I think that’s because a lot of the major development that needed to happen in Season 3 was already handled. Not all of it, though. There were still a few Bellarke moments. However, the one that stuck out most to me was when Clarke woke up after being deposited back on the ground (after Luna kicked them off the rig) and she pulled out the chip to see if it was still there before looking back at Bellamy, just to find him already looking at her.

He’s obviously noticed her attitude toward the chip (and L.exa) and has most likely put together the pieces as to what happened in Polis. As you can tell from the gif, he gives her a slight nod, an acknowledgement of what he has gathered and her feelings for L.exa, and then turns away.

I think this moment is important because this is the moment that Bellamy accepts Clarke. He accepted her for who she was in Season 1 and in Season 2 - he was one of the few people who did (god knows Finn and L.exa never learned to) - but this is the moment where he recognizes that Clarke’s time with L.exa, on her own, and in Polis have changed her. She’s still Clarke, but she has grown in ways he couldn’t come to terms with in 3x03 (in part because she didn’t explain anything to him at the time). This is him coming to terms with who she has become, and loving her anyway.

Those are the major points in the evolution of Bellamy’s feelings for Clarke, in my opinion. This is a very, very complex topic, and I definitely haven’t hit everything or delved as deeper as I could have, if given enough time. I hope this satisfies your question and that it is what you were looking for. If anyone has a different opinion or anything to add, please do so because I know @moresassythanclassy wanted me to signal boost this!