Ive shared several past girlfriends with my two best friends. It started one drunken night in my early twenties, I caught a girlfriend fucking my friend after I had passed out, I woke up and couldnt find them in the house, so I went outside and they were in the backseat of my full size bronco on a hot summers night. I wasnt mad or jealous as I wasnt in love or anything and he was my best friend since we were like 5, so standing outside jacking off and hearing him pound her and make her cum in my backseat was so fucking hot.
We both started sharing girlfriends after that, sometimes all 4 together, other times one of us would fuck the other ones gf 'behind' each others back, as far as the girls knew. It was even hotter that way, fucking them when they thought they were being dirty and sneaky.
My other best friend got into it years later with my long term gf at the time. I watched them more than I joined during that episode, it was just hot, either you get it or dont.
Some men get into the submissive thing and letting their women fuck who and when they want, I was never like that, it was mutual and didnt have a fetish feel to it, it was just one big party.
Ive never done it with girls Ive been in love with though and I dont recommend it, her getting pounded by one thats bigger and can go longer isnt going to be good for a serious relationship.
You gotta be 100% confident in yourself before letting someone fuck your girl. If you are it is one of the most erotic things you can ever do.
Ive never had any girl not totally love it, even if they were initially reluctant or skeptical. They were always surprised how much they loved me watching them fuck. They liked showing off with another cock for their man.
It always made for hot dirty talk whenever we were alone too.