You have a girlfriend named "Karla"

Karen has a brother named "Karl" sometimes when you have a date with Karla, Karl will be there too..

One day you stay at their house

While Karla sleeps you and Karl kiss. You moaned a little and stopped him

"What~?" Chuckle "Are you afraid your girlfriend will wake up?" Karl said.

How did this happen? Karla throws a celebration for Karl because he's graduating and you drink yourself to the point of blacking out