Advice wanted:, suicidal friends? Options

[imperfectionistx]

In relation to the last topic I posted,
My most recent ex keeps telling me he is going to kill himself.
Which makes no sense to me, because HE'S the one that keeps leaving me.
He ends up saying he hates life and wants to die (after dumping me and blaming me for ruining it for him, for whatever reason).

I'm (pretty) sure he's serious, because he HAS tried to before, and luckily he's still here.
But the thing is-- how do you know when they're not serious?
Sometimes I question when he is telling the truth, but I'm afraid to not believe him because that might be the time he actually does it (and doesn't live through it).
My last-last boyfriend was the same way, but he lied about it.
He always would tell me that he was going to kill himself, or he was in the process of doing it. But it was always a lie. I'd panic and call him and his parents non stop, every time he said he'd do it, but he never did. Never even came close.

This time, I'm not so sure when my most recent ex is being serious or not. As of now it's frustrating and frightening because it keeps happening and I dont know what I'd do if he actually followed through. Another one of my friends was like this also. We discussed suicide (morbid as it may seem) a couple times. Now, she's into drinking. I worry about her, but sadly we are not as close as we used to be.

I'm unsure of what to do about these kinds of situations. I'm concerned but don't know if I'm being concerned for real reasons. I mean, I know that if anyone talks like that, you SHOULD be alarmed, right? I'd think just about everyone has contemplated suicide at some point in their lives. But what if sometimes you really think they're all talk?

Are any of your friends (or bf/gf) like this? How would you handle the situation? How should I?