"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.
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Tell him being his gf is not working out for you BUT if he gets help with his depression you know he will find a girl that would love to be his gf
A relationship is for good and bad times. My opinion. However, if you hate it leave. I just feel bad for the guy. Usually if you love someone you are there for them. If you're not in love anymore I guess it's a different story. On the other hand, if he gets better, healthier and happier you might want him back but he prob won't.
Before you just end it , ask yourself if you love him. If you do , then why not tell him that you love him but this relationship can go no further if he doesnt seek help. If he truly wants to feel better and be the man you need , he will do what he needs to do. Every community has a mental health center where resources are available even if you are uninsured. The rest is up to him. Dont feel guilty because you cant " fix" him . It is not your job. Relationships should be mutually fulfilling, not one person " saving" the other. That is a dead end street. Good luck to you whatever you decide . Your obviously a caring ,loving person and you deserve to be happy.
I was going through something very similar and realized at one point that I was becoming co-dependent. If you love him, you can support him without taking on all his burdens. You need to learn to keep a safe distance from his unhappiness. Even if he can't give back to the relationship right now, is he at least showing you signs that he is trying to help himself? If he doesn't recognize the problem, and isn't willing to help himself, very little will change and breaking up is the only right answer for YOU.. I know EXACTLY what you mean about rehearsing the break up over and over. Instead of breaking up, try putting a little bit of space between you to show him that you are not his therapist and also give yourself the time to rest and regenerate so that you can be supportive in the right way when he needs it.
If u can't go through with it it's because you love him, simple as, ask yourself why your not happy, and speak to him about it, it's a two way street how's he gonna know if you don't tell him, at least give the guy a chance to change things by telling him what's up. Emotionally stable or not if he loves you back things will change.