When I was in college, my gf shared me with her roommate all the time. I was very lucky that my gf was not the jealous type as she just asked that I keep myself limited to her and her roomie. That was an easy promise to keep, as my gf was sexy as hell and her roomie wasn't far behind either. Both girls together or singularly was always hot. My gf loved to come to her apt and catch me fucking her roomie so she could join in. But she also liked for us to be fucking and her roomie came home and joined in. It was a wild and crazy 2 years.