What will you do if you know your girl-friend is cheating on you?

well it all depends.. if she is someone u really think is 'the one' then maybe u have a talk with her and see why she cheated.. is she unhappy? made a bad mistake? really is no excuse but i think rarely there are cases where it was a mistake and that person will regret it forever n keep themselves faithful.. but most cases i think they will cheat again.. specially if forgiven once for it.. but it all comes down to how strong u think the relationship is.. is it worth tryin to save? thats the main question n then u can work from there..