What should I do???

so my boyfriend that I've been with for 6 months now is super depressed and says he wants to die. I'm really shook up about it all and I keep trying to help him feel better. I know he's told me in the past that he's been depressed all his life and he's tried getting professional help before but it hasn't helped much. I guess all I'm trying to get help here on is what I should do? I really don't want to loose him, we're in a pretty serious relationship and we've been through a lot. It's been so stressful mentally because I'm so nervous I'm going to come home one day and walk into something or get a call. I'm so lost and I don't really have anyone to talk to. Ahhh what should I do!?