Rather than being p@ssed off at her about it, how about being nice to her about it?
I'm not exactly sure where you feel insulted by what she did. She told you she was staying over with the friend and son and she told you when she'd be back. It's not like she stayed at the guy's house alone.
I think you're letting all the stress of the talk get to you. Right now she's looking at doing things that take her mind off of your sitch. Whether its drinking or hanging out with someone, it's what she's going to do. Confronting her about it isn't going to do any good.
M-43 W-40 2D - 9 and 5
Emotion, yet peace. Ignorance, yet knowledge. Passion, yet serenity. Chaos, yet harmony. Death, yet a new life.