My Girlfriend’s Triangle

[Fuumayami]

Does this make a good premise?
Girlfriend is part of a friend group that includes her, a female friend, and a male friend. They are all best friends. Both women are infatuated with the male friend, but he’s not the type to settle down. Still, that didn’t stop him from sleeping with both of them. They often have threesomes and sometimes the girls have lesbian sex. Wanting a real relationship, girlfriend meets MC have been together for 3 months and it's been really good.
After this new found revelation, boyfriend is conflicted. He wants to make this work, but should he? He'll always wonder what they are doing. Girlfriend doesn't want to lose him and needs to find a way to make him stay. What she hasn't told him yet while they first started dating and weren't official, she was having sex with male friend and having threesomes.

How does boyfriend find out?
Could be girlfriend tells him or in a casual conversation, the topic comes up.

Thoughts?

 

[IARainman]

So, “boyfriend “ is a male outside the friend group? So, in total there are two women, two men?

I’m lost on the series of events. Seems like there are two revelation points where boyfriend comes to realize girlfriend likes sex with other people.

So to simplify:

Girl is part of a group of 3 friends (2F, 1M) who have sex in various configurations with each other. Boyfriend comes along and girl becomes gf. He comes to find out her friends are fucking her when thought they were monogamous.

So, the question is how he finds out?