one should not agree to be in an open relationship (i'll assume that's what it was, given the commentary) if they're not able to handle such things. most people aren't able to. that's not a bad thing. but that just means that you should be mature enough to recognize your own abilites and tolerances, and say "no" when things get to be too much.
cheating, Y s right, is not acceptable. if you ended the relationship when that happened, kudos to you. but from your statements, is sounds like you still have too much of an attachment to this person. that's not good. if you were that hurt, you need a clean break.
beyond that, if this is a new "boyfriend wanna-be" that means you are the OLD boyfriend (wanna-be) and no longer a valid part of the equation.

um, duh? this is what people do now days. there is no such thing as permanence and you knew what was what going into it. open relationship mean anything to those brain cells?

Wow. You are disillusioned and unhappy. People in "open relationships" are in the miserable minority.

Cheating is, always has been, and always will be, totally unforgivable.

fxxx you guys u dnt know me and she cheated

I wasn't the OP, but I definitely fall into the 'need laid' category!

well, someone's bitter