She says she's going to kill herself so keep her around (you'll want the sex, but use a condom now). However, turn that heart to stone and get your resume out. The second you have prospects pack her shit, put it in a locker, fuck her one last time then give her the locker key and a pack of grape Kool-Aid.
Seriously though, once a cheat, always a cheat... and EVEN IF she never cheated on you again, you would never believe that she didn't because infidelity is a relationship wrecking ball, it just keeps swinging back and forth and will surface years later. The trust is gone and the whole point of a relationship is that you are with someone that you can trust and share everything with. You guys can't even trust her with her most intimate gift. Alcohol don't make your clothes fall off and lack of inhibition don't make you hump people you wouldn't have anyway.
Drop her or you are a fool. As for suicide, tell her to go talk to the guy she fucked, he might be able to console her.