Bro it will go something like this:
She will be pissed and after a few days you will ask "what's wrong?" Then she will say something like "I bet you really enjoyed fucking stephanie". You will say: What the fuck...This is what this is about? I thought you said it was okay to have a threesome! She will say: Yeah, I bet you had a good time! There will be a lot of name calling and finally you will call her a stupid bitch and she will throw a John Grisham book at you and tell you to get the fuck out.