From what you say your girlfriend had one night stands which were fully consensual she was not being used she was having the enjoyable sex that she wanted to have this is the new world that men need to understand if they can call themselves progressive.
Also while it was my first one night stand it wasnt the last it was my best friends birthday party and i was only looking forward to a fun night with hours of dancing but the night took a completely different turn and introduced me to the world of casual sex.
I am dating a girl i very much enjoy being around and want to be with my problem she had a onenight stand without getting into details basically everything except sex with one of my best friends about 6 months before we met.
I really liked the girl i had that onenight stand with and i felt like i ruined the dynamic of that potential relationship by going through with.
Your girlfriend slept with your friend but ended up committing to you that means that she saw something special in you that she truly valued and liked you are special to her this one night stand was not.
So you want to hook up with a girl and get a onenight stand go out lock eyes with her walk up to her smile at her say hello then not.
Most of my friends were surprisingly sympathetic to my cause and even offered to phone up a friend of theirs some were out of commission due to cyclical maintenance issues but they offered.