Husband problems please help!!!!

Ok well we are happily married now. We have been together for almost 10 years. About 7 years ago we got drunk and I ended up doing something with a friend of mine(girl on girl) my husband walked in and tried to intervine, well I told him no. It is 7 years later where he swares I cheated on him and owe him a 3some...he said it is only fair, and it has been a fanisty of his for a while. I don't feel comfortable doing this but he keeps on reminding me...I don't know what to do. He sends me pics of 3somes and asks about my friends...what advice do u have????!?!