I was suicidal through my entire teens (from 12 to 20), and have been off and on throughout my 20's and early 30's. For the most part, I didn't talk about it...although I'd occasionally "hint" at it, in the hopes that someone would try to convince me I was worthwhile enough to stay alive a little longer.
My ex was also a depressive, but of a very different sort. He never wanted to address his problems, and treated any attempt to help him as being dismissive of his issues (ie. somehow the idea that depression was a problem for him meant that he didn't have any "real" problems, and it was all in his head). He was also a first-class emotional manipulator...and he played the suicide card a few times toward the end..."if you leave, I'll have nothing to live for, I might as well kill myself" and all the rest of that crap.
If your dp (ex dp?) is trying to put the responsibility for his suicide on your shoulders, then he's being a manipulative jerk. More likely, he's trying to scare you badly enough that you'll be guilted into staying. Someone who says "if you loved me, you'd stay" in that kind of circumstance isn't demonstrating any love for you
. A relationship can't run on guilt, and it doesn't say good things about your dp that he's resorting to this kind of tactic. (He may well be genuinely depressed...but there are ways to handle it and ways not to handle it. This is about more than clinical depression.)
Good luck to you!
If you really do want to find out what's going on, then I suggest the police, as well. But, if you do that, don't be surprised if he acts completely bewildered when they show up, and does his best to convince them that you're the one with the issues...that you made it up or some such. That's what happened to my cousin in this situation. The cops thought she
was a loon, and he'd been sitting in his locked car in the garage with the engine running!