Havent been able to find this story since the new story searching functions came online.
A young man wants to go to a concert but has to take his aunt and her girl friend with him if he wants to go. During the concert he first ends up feeling up some girl who thinks he's his boyfriend. After almost going all the way he gets pushed back to his aunt and her friend.
Then he starts making out and feeling up his aunts girlfriend for some time. Eventually they go back with some form of public transport where he starts having sex with her.
Eventually he also has sex with his aunt after her girlfriend was dropped off somehwere