A few years back I went on a ski trip with my girlfriend, two other couples, one of my girlfriend’s friends (who had a boyfriend who couldn’t go) and a single male friend of ours - 8 people total. The parents of one of the guys who was a couple owned a big 5 bedroom house in a ski resort area that I purposely won’t mention. The first day the guys all go skiing and the girls hang out in a bar at the resort. We’re all good skiers and push each other; I hardly ever fall so I push things too hard and of course this time wiped out pretty bad. I called it early while my friends still skied and went to the bar to meet up with the four girls. We were all drinking and having a great time; soon thereafter the other skiers show up, have one drink and we head back to the house for more food and drinks. My girlfriend is very drunk after awhile and I eventually put her to bed in one of the two downstairs bedrooms. There’s a full bathroom downstairs and two bedrooms - my girlfriend’s single female friend has the bedroom next to the bathroom and we have the other one. The other people all sleep in the bedrooms upstairs. My girlfriend eventually passes out, we all go to bed, after probably a couple hours I wake up to take a leak. It’s pitch black in an unfamiliar house so I walk slowly to the bathroom at the end of the hall. I go in and shut the door before I turn the light on so I don’t wake people up; do my business and turn the light off again before I open the door. I feel along the wall for the rooms - here’s the first one I say to myself, now the second one - my room. I go in and lay down on the bed. After laying down for a few minutes I feel a hand rubbing my thigh, then up to my now getting hard manhood, she starts stroking it, and I thought “you go girl, wake up from being passed out and you’re ready to get it on!”. I flip her on her back, go down between her legs with my face and just lap up her now soaking we’re pussy. She’s getting off and I’m thinking “different taste, different smell” but don’t connect the dots until I start fucking her and feel her tits. My girlfriend has fairly big, very nice tits and these were smaller than I’m familiar with. I have that “oh shit” moment - who is this, how did they get in my room, where’s my girlfriend, etc? My girlfriend’s friend is more athletic, ran track in college, and I realize it’s her. She’s getting off - pillow over her head to muffle the sounds of her orgasm. I pull out, stroke a load all over her stomach and tits, and get up to go out of the room. Here’s where it gets interesting. I don’t go to my room immediately in case she’s listening to where the person that just had sex with her goes so I go upstairs rather loudly so if she is listening she’ll know I went upstairs. The girl was flirting with the single guy a little earlier so I figured she probably thought it was him. I go upstairs, hang out a little, grab a bottle of water and go back to my room. Got it right this time. Get in bed and - no girlfriend! Oh shit!! Have I been caught? After a few minutes she stumbles in, asks where I was. I said I went upstairs to get some water and offered her some. She said she woke up, thought she was going to throw up, realized I was gone and waited a long time for me to come back and just found her way to the bathroom herself. We must have just missed each other, or she went into the bathroom when I was having sex with her friend. The next day when it was light I realized my mistake - there’s a closet right next to the bathroom that in the pitch black I mistook for the first bedroom. I went to the second one which was the one with my girlfriend’s friend. The issue is never brought up. There’s an outdoor hot tub at the house that I said we should go in - I was sore from my wipeout the day before. Two of the guys and my girlfriend and her friend are going too. I take my shirt off, and my girlfriend says “where did you get all the scratches on your back”? Her friend looks at me quizzically - I immediately say “I told you I wiped out yesterday and that’s why I quit early, must have gotten dragged on my back for a long way”. The two guys just added “yeah, that was a rad wipeout” etc. so I think I covered up the nail scratches down my back pretty well. Since then, we still all hang out together. I’ve become pretty good friends with the boyfriend of my girlfriend’s friend who I hadn’t sex with that night, but as far as I know the issue has never come up. Not sure who she thinks she had sex with that night - I just assume she thinks it was the other single guy in the group and that it was just a one time thing. I love the story but for obvious reasons don’t share it too much. Lol Thanks for reading!