Wow ... I thought people agreed on that sort of arrangement *before* being serious? Oh, and BOTH people have to agree to it. Not a great way to go about things; you'd be right to get rid of her.

Who are these people who call "Surprise! Open relationship!" when they're caught cheating? Is it a common thing? Do they honestly think the other person is going to buy it? "Yes honey, we're in an open relationship. You were meant to figure this out through your psychic powers, except I'm the only one allowed to sleep with other people. Especially people close to you. Also, I'm much more of an STD risk than you thought I was, having told you nothing about the above, so you might want to get checked." Sorry OP - she either thought you were that gullible, or she's an idiot. Either way, neither she or the "friend" are worth your time. Walk away.

I didn't know that dogs could play twister...

why is it always with the friend??wtf??

I this point I believe it's perfectly justified for a guy to sucker punch a girl in the face. But that's just me.

These hoes ain't loyal

Stuck in traffic? That's such a 'guy' kind of excuse. I find many women are usually smarter than that if they don't want you to find something out.

Cut that chickens head off.

Stuck in traffic sounds like a metaphor for a gangbang.

Dump her