"Then you don't get to walk away either," he turned it around on her, just to make the point clear. They were both responsible. Monty was just as culpable as they were, though it wasn't a subject he was going to broach with her right now. He knew she wouldn't want to face the idea that gentle, nerdy Monty was a killer now too. Even if it was the Mountain that did that, Clarke would want to take it on as a personal failure and he didn't want to tackle that bridge - it was a big enough victory getting her to let him take his fair share of the burden. He would take that and run with it.
"Because I need you," he spoke again, the words not only a true confession, but an echo of what she told him once what seemed like a lifetime ago, even if it was only a few months. "We all need you," he reminded. She brought him back from the brink once before, so maybe he could make it clear that's what he wanted to do for her as well. And truth be told, he did need her. He needed the drive she could give him. Bellamy knew he could inspire the others, he had given plenty of rousing speeches to boost morale or win people to his side of things. But without Clarke to direct his hand, what would he be winning them over to? He was more of a general than a leader.
He needed her on a different level, too. He needed her, in a sense, like he needed Octavia. Another person to complete him. Octavia was the foundation he laid everything on, who he built his world around. He needed Clarke to be everything else. The sky, the stars, all that poetry his mother would read to them about great men doing great things for greater women. So he could bear the nightmares and the ghosts of the people he'd killed - the people they killed. He could keep killing people. He would keep killing people. For Octavia. For their people. For her. Yeah, he was a monster, but he was starting to think it wasn't the sort of monster his mother wouldn't be proud of.
"We've all made a lot of hard calls. We call Dante a monster or Cage. But we've all got blood on our hands. You. Me. Octavia. Jasper. Monty. Miller. Raven.... Lincoln, Lexa," he added the grounders to the list. Finn, Murphy - he didn't add them to the list. "Your mother," he did add Abby belatedly. Which of them hadn't been responsible for at least a handful of deaths by this point? He trailed off, because he was making his way toward a point, but Bellamy suddenly found himself uncertain as to whether or not he wanted to get there. He clenched his jaw, the muscle jumping in his cheek for a moment. No, he needed to do it. Because saying he needed her wasn't enough, not anymore. He hadn't been devastated when she chose to walk away just because he needed her. He didn't need to help her shoulder the deaths of those people just because she was a good leader and a good friend.
"Clarke," he shifted to face her fully from where he'd been sitting at her side. "When is a monster not a monster?" She could take it any way she wanted it. She could even deflect it, repurpose it, make it about her mom or Octavia or whatever, but Bellamy took in a breath; "When you love her," he pointed out quietly.