This happened about 4 years ago with an ex girlfriend of mine.
To give you some background at the time I was 26 and she was 23. We both really enjoyed working out so as such were very fit. She was on the shorter side- around 5'2" with lighter green eyes and dark brown hair and around 110lbs. She was very lean but still had a shape to her. I am 5'10" athletically built with a solid chest and shoulders. Back then I had quite ripped abs….not so much anymore unfortunately.
Anyways, one night we were having dinner and of course a few glasses of wine. We had been dating for about 4 months at the point so we're getting pretty open with each other.
Being young, fit and relatively new to each other our conversations often turned to sex and this night was no different. We started sharing our fantasies and discussion what we both had always wanted to do sexually etc. Her #1 ended up being to be tied up during sex. Mine was to share her with another guy in a mfm threesome. She started asking about that and we got away from hers.