The time my GF's sister (F27) walked in on my GF (F27) and myself (M30) fucking

This happened last week and I can't stop thinking about it. My girlfriend and I were at her place that she shares with her twin sister. It was about 10pm and we were getting hot and heavy in her bedroom. Generally we take our time with lots of foreplay and just enjoy each other. We were making out and i was two knuckles deep in her pussy while she was stroking me off when we heard her bedroom door open.

Her twin sister had walked in and we both pulled the covers over ourselves in shock. To our surprise her sister said "i could hear you two moaning and wanted to come have a look for myself" keep in mind my GF and her sister are extremely close but this is the first time anything like this had happened. My girlfriend leaned over to me and said "should we let her watch?" Me being the complete horndog i am said "yes, absolutely"

Shortly after that we pulled the covers back and my GF went down between my legs and started to suck my rock hard cock. All while her twin sister had pulled up a desk chair in the corner of the room and watched us with a hand down the front of her sweatpants. Watching my GF go to town on me and being able to look over and see her twin going to town on herself was an insane experience and one i will never forget. We continued for a few minutes before I told my GF i needed her pussy. She turned around and got on her hands and knees while looking at her sister and i positioned myself behind her as i entered her pussy. I started fucking hard since i was sooo turned on at this point. Both of us staring at her sister who had taken off her pants at this point. Being able to fuck one twin while the other was getting herself off to the sight of us caused me to blow my load fairly quickly. I pulled out and came all over my GF's ass and had one of the best orgasms of my life. Her sister finished and said "that was fun, maybe next time i can be more help" she pulled her pants up and left the room.

I've talked to my GF about a potential threesome but we have yet to cross that off the bucket list. Wish me luck for the future.