Addison was married. Well more importantly she was married to a well known well respected doctor in Grey's Memorial Hospital. She was married to Derek Shepherd.

You knew that when you started sleeping with her. But now you're sleeping with a married woman and dug yourself too far to stop.

Derek had left for the week to Illinois for a surgery. So you took his spot.

You were at Addisons house as she was getting ready for work,choosing her outfit for today just in her underwear.