I would be filled with rage and end them. Permanently. If I can't have them all to myself then no one can.

End their life.

lol, obviously I would just move on, plenty of fish in the sea

Dump them without a doubt, I have better things I could spend time on than a lousy cheater.. :/

Curse them out very loudly in a highly populated area so everyone will hopefully know what an asshole they were and then slap them HARD before storming off and never talking to them again!

I would cry my heart out, but I could never be able to forgive them for it and never be able to trust them fully again, so I'd have to break up with them. TT~TT

Probably kick his ass.

Break up with them and hope they're happier with the other person.

Honestly? Wonder where we went wrong...

I think i'd just do my best to move on, I'd rather find someone who's actually worth my time then be hung up over someone that clearly didn't care...

I'd probably fight them and kill the person they cheated on me with.

I'd cut them from my life.

I'm used to it. I'd just break up with them and move on.

I would end them.