"I need to take care of him" is not a good reason to stay with someone. And you know that.
A girlfriend is not a replacement for therapy, and therapy is what your boyfriend needs. Having you around is not going to make him healthy, so you shouldn't feel like you need to be there providing psychosocial care that you're not qualified to provide.
You're feeling stress and unhappiness because you're pouring energy into a one-sided relationship. That is making you even more unqualified to provide the care and support you're already unqualified to provide.
For your sake, and, yes, for your boyfriend's, you need to end this relationship. You're doing him no good by being there, and you're not doing yourself any good either. Whenever a relationship feels like a job, you need to stop being in that relationship. You know what you need to do. He will be fine without you.