Specialmom is 100% right.
Also...no matter WHAT he decides to do...even God forbid if he would take his own life, that's NOT on you. He's definitely using his problems as emotional blackmail to keep you around. You need to put a stop to that. If you don't want to be with him (which I agree is probably best, and safest), you leave, simple as that. HE is responsible for his own actions.
If you notify the proper people (authorities, doctor, etc)...you've done your part to try to get him the help he so obviously needs. After that, it's out of your hands.
If you have text messages or voicemail messages where he is making these threats of suicide...go to the police and show them. They will know how to handle it from there.
Best of luck...I hope he gets the help he needs. YOUR safety needs to be your top priority, as SM said. Dont let him trick you into putting yourself in harms' way. That happens all the time. He may something like, "Ok, I'll get help, just come over one more time so I can see you, and THEN I'll get help." You go over, thinking that's going to be it, and he'll get help...meanwhile, you walk into a trap...he could harm you, or worse. He's NOT thinking rationally, and desperate people do desperate things. Protect yourself at all costs.
Oh my goodness, I"m so sorry. This must be terrifying for you.
Okay, well ---- I will tell you right off that he needs to be admitted for inpatient care. How intelligent or functioning (except when self harming and threatening you?) he is, that has nothing to do with treatment for severe depression. Inpatient care provides medical help along with support services for someone in grave danger which he sounds like he is. He'll work with a psychiatrist, be offered medication, be given coping mechanisms beyond self harm/threats, he'll have support group help, etc. All the things someone needs to turn their life around when they are deep in the throes of depression. He really really needs this as he sounds like a danger to himself. Working with an in hospital psych team isn't a punishment but rather a way to help someone get better. He needs to get better.
And have you ever thought that perhaps you are in danger as well? Murder suicide is real hon. He could easily decide to take you with him. This is not a good situation at all.
You can call his psych if he has one or doctor and tell them that he is self harming, threatening suicide and you believe he will carry it out. You can call his parents and be very direct. You can call the police. A 72 hour hold can take place if they fear for his life or yours due to his mental health.
It's the right thing to do in order to get him the help he needs.
If you say you are being held hostage, you aren't. Time to leave. If you have done your best to get him the help he needs (called psych, parents, police) for his severe depression ---- you are then free to go. You are not responsible for 'keeping him safe/alive'. His depression is ruling that decision and that is what needs to be treated. Your leaving would not cause a healthy person to self harm and that is what you need to know.
So, attempt to get him help and then have someone with you when you tell him it is over/get your things. I wish you well. I wish your boyfriend well. He needs help. good luck