First, sorry about my english and I hope someone will understand me x)
That's sad. If I meet guy who say that he is suicidal, that isn't problem to me. Even when I'm doing good I don't never think like that, but that's probably because I know what being suicidal is...
Probably some people think that's too much for them, they can't handle that information and get scared. They don't know what that means and maybe think you are going to do it soon (and don't want to be in that situation) or think suicidal people could be too heavy with all their problems. Dunno. They maybe think that's all what you are and don't see how great you still are.
You can think that's also good thing that they say right away what they think, you probably want to meet someone who is totally ok with you and your thoughts and you don't need to pretend anything.
I'm glad that I have nowadays someone who accepts me as I am, but I had situations like that and it's not fun... You tell that you are suicidal and little mess and someone just disappear.
I think that's kind of same how do men behaved because I am plus size when I was dating... First they thinked I'm beautiful, but when saw all pics they realized that I'm plus size *puff* gone. Only because one thing what is part of me. Or if I'm out with friends in the bar, guys come and tell me that if I weren't plus size they could be interested me (what I even do with that information?).
And no, how you look isn't same thing that being suicidal so that was probably bad example. Sorry.