Who is in the wrong

A little back history : my bf and I have been together for 6 years and always hangout together and have a lot of mutual friends. Our one friend has been my bfs friend since they were in elementary school. We hangout quite a bit. Our friend has a gf of 2 years whom we have invited to hangout so many times. Finally after a year of trying she hung out with us twice. Both times she made a scene, started a fight between them over little stuff, and was honestly just rude to us despite trying to be very welcoming and excited to finally have her over. After both times ending badly we stopped inviting her and our friend agreed to not invite her bc it just wasn’t working out.

We were planning a weekend trip out of state to celebrate my bf and our friends 21st birthday but know he isn’t going because she is mad at him for not being invited (even though she is only 19 and can’t go out anyway) and told him he isn’t allowed to go( they didn’t have any plans ahead of time either ). “I won’t be able to go my boys me and ****** can’t seem to come to a agreement with it. I’m just not gonna make any kinda plans to go out like that anymore bc I always have to cancel. I are sorry”was his response to not being able to go. Every time we try to do something as a group he always ends up not going because she is mad he is doing stuff with us and not her. Which she would gladly be invited to if she wasn’t rude the whole time. I could understand if it was just me and him but it’s our group that has been friends before they even met and we have tried so hard to include her. Any insight on what to do so we can have fun as a group still? I know it is their relationship but it sucks seeing our friend so down all the time trying to make her happy but still have fun and hangout with his friends.