Let me know if there is already a story out there like this.
A girl is in school either high school or college. She is having sex with her boyfriend. She wanted to do something different. She had her boyfriend tie her up possibly in the doggy style, but in a locker room or some other room that at one point of the day would have a lot of people in it. She picked the time they would do this. During that time of day people are usually gone. After they had sex one time the guy had to leave for some reason. They had planned to have sex again so he didn't untie her. Before he came back a group of guys came back and had their way with her. The boyfriend comes back after everyone has had their way with her and left. He starts to apologize for being so late when he sees the condition she is in. She also ends up pregnant.