there's no way to know for sure; different people handle emotional burdens like that in different ways.
generally speaking, though, I'd think that knowing someone you loved intended to kill themselves (and also not sympathising with them, ie. a terminal cancer patient) would instill you with a sense of helplessness... the longer it goes on, the more emotional stress you're under.
that said, I have a friend whose mother has serious mental issues and has threatened to off herself for years. after a while, a part of him started to wish she'd just do it, because after such a long period of not being able to help and her not being able to help herself, he started to believe (at least partially) that if things weren't going to get better it may be prudent just to cut her losses, so to speak.