I feel your pain RP. It's a tough spot to be in when you need to care for someone else and your own needs conflict with what they they feel you should be doing to comfort them. I've been in situations before where it felt I was getting sucked into the black hole of their despair instead of me pulling them out into the sunshine. Sometimes, and I'm not saying that this is what you should do, but sometimes you have to put a foot down and say, " it's time you take a shower, get some fresh air, see some people, stop being a zombie, and know that I love you very much and I feel your pain, but you've got to stop taking it out on me. I need to be happy too so that I don't resent you when you find your happiness again."
As for the boundary break, it happens when it's an old one. People are imperfect and forgetful. Time will heal that. It's seems to be the lesser of the issues at the moment. (((huggs)))