He fucked the wrong sister
The summer after I graduated from high school I went to stay with my older sister and her husband. I was starting college in the fall. My sister was 21 and her husband was 22. One night while my sisters husband was out with his friends, my sister and I stayed up late. We mostly just visited and watched a movie before going to bed. We were both in their bed talking until we fell asleep. At some point in the night her husband came home. He climbed into bed without turning on the lights and snuggled up to me while I was sleeping. I woke up to him running his hand up my waist and cupping my breasts. I was still half asleep when he slipped his hand down my pajama bottoms and began fingering me. At this point I was wide awake and was thinking, does he know he’s got the wrong sister? It felt good so I didn’t care. I reached around and started stroking his cock, he was rock hard. I pushed my pajama bottoms down and let him fuck me from behind. He came in me, then we both fell back asleep. The next morning neither of us said anything about it, and have acted like it never happened since.