Didn't he also kill a lot of people his sister tried to save ? Like he is a mass murderer right? And he didn't treat lincoln like he was one of them, he switched up very quick not even thinking about the fact that lincoln is his sisters partner. Lincoln was in jail with the others days or hours before he got the death sentence because he helped the rest escape. People just talk about the fact that octavia is angry about Lincoln. But its not just his death, its everything that lead to that point. She was also angry at monty and the others but its different when its your sibling who basically lead everyone else. The one that is supposed to be the older and wiser one and always said he does all of it to "protect you". Its not always a good thing to have someone like that protecting you, add a bit of trauma and you got yourself an unjust war. He also almost killed Indra who plays a mother role to octavia in a sense or at least she accepted her and thought her a lot. She wouldn't be so opinionated and strong if it wasn't for Indra, since she had to prove herself over and over to be accepted. Lincoln tried that too on the other side but ended up with bulled in his head because he could never be trusted as a grounder in their eyes. And if you care about the grounders like Octavia and feel connected to them, you think about their pain which also makes it your pain in a sense and your brother is responsible for a lot of it. She can hate Bellamy for the rest of their life's in my book and Bellamy would have to live with that. He killed innocent people that were send to protect them with machine guns like a paranoid coward. Pike and him lost people which set all this off, same with Jahar. It makes sense for pike and jahar since they had no experience with grounders but Bellamy worked with them and his sister was in love with one. So for Bellamy? Is it really about protecting her or anyone or is it just his ego and he uses octavia as an excuse to go loco sometimes cause octavia can handle herself pretty well. Its like he is stuck on the arc and thinks about a helpless octavia who basically grew up under her floor, she came out of her room just a year before they were sent to earth. If octavia doesn't forgive him, the person he only cares about, how can he forgive himself and still think he did the right thing regardless of all the deaths he caused.