I'll kill myself if you leave me.

So a friend's friend is having a bit of a situation with his girlfriend. He wants to break up with her, and she is threatening to kill herself if he does. Apparently she has attempted to harm herself, so she sounds like she's pretty serious about it (not that anyone should ever be cavalier about someone threatening suicide).

I don't want anyone to hurt themselves, of course, but I wouldn't want anyone to stay in a relationship only because they're being guilted into it.

So I'm asking you guys what is the best thing to do? I suggested to my friend that her friend call a suicide help-line, and perhaps contact a friend or her parents to monitor her/be there when he breaks up with her so she is not alone during the most sensitive time of the break up.

What am I overlooking?

I had an ex boyfriend who threatened to kill himself, but was not actually harming himself. I finally said to him (after a year and a half of the threats) "if you kill yourself it's not because of me. You obviously have problems that aren't about our relationship." (Clearly I wasn't the most sensitive 18 year old, but it had gotten old.)

Help?