Relationship problems

I have a long distance relationship with my boyfriend. He's schizophrenia bipolar and i have depression and massive social anxiety. I don't normally do this but I'm kinda at a loss right now. My boyfriend just started lithium. He doesn't involve me in anything that's going on because he doesn't want me to get hurt. I've tried everything to be there for him but i feel like no matter what i do nothing works. it's hard not to get all upset about the whole situation. I know it's not something you can just fix but I feel like I can't do anything. Two nights ago we had a serious talk about us. We both don't want to break up but he says that it might be better for me to leave because he doesn't know if he'll get better anytime soon. He also doesn't want to make promises to me he can't keep. I don't know what else to do. I really don't want to leave him.