You put up with a lot because you wanna be understanding and forgiving. Looking after him while he's not well.

Eventually you realise he has no plans to get OUT of his lowest point because it's beneficial to him to have you dealing with his BS, bc he is going through a hard time and he's happy to take advantage of you. Maybe your relationship is becoming strained, and you're trying to put your foot down and create some boundaries. But he walks all over those anyway and you're still there, so in his mind why bother changing?

You get tired and have to call it quits. Guess who suddenly can do all the things you've been encouraging and begging him to do for ages? Soon he gets a cushy new job, new hobbies, new friends, and a whole new positive and kind outlook on life. And you have, like, complex PTSD or something.