I (20 M)have known my best friend(20 M) for 15 years and he has been dating his girlfriend(20 F) for 4 years. Over the years me and her have talked alot and have gotten to know each other pretty well. One day she sends me a pic and when I open it, it was a picture of her spreading her ass. I didn't know what to say or whether I should respond or not. 2 months later one of our friends was having a party and she asked me if we could talk for a second. She told me that she didn't mean to send that photo and she is really embarrased and I told her to not worry about cause it was just a mistake. She thanked me and gave me a hug for understanding and wondered if I could be designated driver for a few people, I accepted since they were on my way home. Towards the end of the party my best friend was making jokes about me and a girl I was close to and how we never dated or fucked. He was making me laugh and his girl friend came over and started laughing with us about it. She asked to sit down since I was the only one in a chair and I went to stand up and my best friend said to stay there and she can just sit on my legs. I still went to get up but then she sat ontop of my lap. I didn't want to move since I kept thinking about how she might feel my penis if she moves her butt. She wiggles her butt and I start to get hard and couldn't try to hide it or move it. As she wiggles her butt again I could feel my penis sitting between her ass. I knew she could tell since she stopped moving and was quiet. Eventually she gets up and I quickly try to hide it. As we get to the car she asks if she could drive since she is the most sober out of all of us. I agree and hand her the keys. She starts driving and we stopped at my best friend's house and he asks me if its ok if I drop her at her place and I said its no problem. So she continues driving and I wasn't paying attention to where she was going but we stop and she turns the car off. I look up and notice we are in the middle of a car park. I ask her why are we at a car park and she tells me that she just wants to chill out for a second. She asks if we could get in the back seat and open the sunroof, I accept and as I'm sitting there she decides to lay her head on my lap and look up through the sun roof. We talk about how nice the sky looks tonight and she just asks me if I have had sex before. Stunned by the sudden question I stutter and say no i'm still a virgin. She gets up and sits on my lap facing me. She asks me what would I do to her if she wasn't dating my best friend. All I could get out was kiss you as she then started making out with me. She began grinding on my lap and said she could feel how hard I was when we were at the party. She hops out of the car and starts taking her clothes off and I do the same. She gets me to hop on the back seat as she is ontop of my lap and she slowly lowers down onto my dick. She holds my ear to her mouth and says I'm bigger than my best friend. She starts grinding and bouncing on my dick and makes me cum insider her. She hops off and asks me if I can continue and I just nod my head. We fuck multiple times giving her creampies and covering her face in my cum. After some time we get dressed and I drive her home as I pull up outside of her house she leans over and kisses me and said she had alot of fun. We said hugged each other and said goodbye as I drove off thinking of what I have just done to my best friend's girl friend and if I can look at either of them again without thinking about what just happened.