If I was in this situation, I’d be saying to my boyfriend that I don’t want this to cause issues in our relationship anymore and it needs to be put to bed by both of us.
Ask him to stop relaying everything that is said and happens in his friendship group to you. It’s not helpful. Men in groups are often like this, it’s all bravado. It’s not as big of a deal as you think it is and if you just brush it off and be normal, soon enough they will move on to something else to wind your boyfriend up over.
Stop fretting about going/not going to him. He’s probably worried you are going to cause some kind of a scene and you obsessing to him isn’t helping either. I think you need to put your big girl pants on and front it out with a smile. It won’t be as bad as you’re expecting.
I can see your dilemma. I am very similar to you in the sense that I feel a duty to do what’s right, but with a decade more life experience, I’d rather just not know certain things now. I’ve been in a similar situation, my husband went on a stag do and his friend cheated on his wife. I toyed with the idea of telling her as she’s an acquaintance, but ultimately decided against it as it’s not my business and I knew it would make trouble for my husband. I wish he just hadn’t of even told me. Your boyfriend should realise that he’s not helping with all this drip feeding information to you.
Some people are generally just more passive. My husband is like this, and would never stand up for me either if his family or friends made a comment. I’ve come to accept this and can see that it’s part of his personality and that aspect of him has advantages. He’s not an argumentative person and let’s things go easily.
I can see how it seems like a huge deal now,but try and move past it (on the outside but also inside your head) it’s not as big of a deal as you’re building it up to be.