[glgs]

This happened a few years ago when I was in NS. I had a girlfriend with 36c boobs and I will sleep over at her place as her parents are very open-minded.
There was this day when I booked out and feeling very tired and I just lay down on my girlfriend's bed to have a nap. My girlfriend share her room with her twin sister and their bed are joined side by side. Both of them have the same physics.
Halfway through my sleep I heard my girlfriend telling me that she is going out to get dinner. As I am sleepy at that time, I just continue my nap.
I woke up maybe about 5 to 10 mins after she left because I was feeling a bit hungry.
To my surprise, her sis was sleeping on her bed which is a few inches from me. She was wearing a oversize T-shirt without bra and just panty underneath. The good thing was that she was fast asleep exposing her panty and part of her pussy lip.
The room was dark and naughty thoughts came into me. I came out with an idea and decided to try my luck.
My fingers started to inch closer to her pussy and touch lightly. I slowly covered her with my blanket with my head under it and start rubbing her pussy lightly. There was slight moment from her sis but I continued and at the same time calling out my girlfriend's name. I knew that she was awaken by my action but I was so horny at that time that I started to finger her.
Since there was no resistance from her and she thinking I mistaken her for her sis. I climbed on top of her but keeping my head in the blanket, I inserted my cock into her wet pussy and start pumping while grabbing her breast. I came in no time and shoot all my cum onto her body. That was when I pretended to get a shock and apologised profusely to my girlfriend's sis. She was shy and asked angryily why I didn't check before doing the deed.
I explained that she and her sis look similar in the dark. She forgave me after lots of apologies from me. We made a pact not to tell her sis about the incident as she didn't want to hurt her. I am still with my girlfriend but sometime I will think of her sis while making out with her.