Married man at work??? His best friend?

I met this guy at work a couple of weeks ago, I could tell he was coming on to me and then we continued talking, he asked me to add him on face book and then I fould out he was married. Come on for real? He is a cute guy and has a great big heart and i know i could trust him with everything i have. I began to fall in love with him, but I cant see myself getting hurt. he is married and has a new born baby at home. One night last week he sees his friend in that parking lot, a guy i had just briefly talked to before and they filled me in about the best friend going through a rough break up. Well I have thought about it and I decided if the friend was interested i would agree to date him. Well, last night mr. married man went home and me and the friend sat in the parking lot and talked for a couple of hours. Now I have a hickie on my neck from the friend I get to face married man tonight at work, What should I do????? mr. married man is one of my best friends now. abd the friend is someone I real like.