My [25F] boyfriend [28M, 3 years] has been banned from being the best man at his friend’s wedding by his ex [28F] from 12 years ago.

I just want to start by saying that my boyfriend is the most calm and sweet natured man on the planet. Nothing really seems to upset him so it’s breaking my heart to watch him come home and stare into space until it’s time for bed because this whole situation has really hurt him.
So, my boyfriend dated this girl (let’s call her Alice) 12 years ago for 3 months. There was no big fight or drama when they broke up, it was just one of those things. But through Alice, my boyfriend met Dave who is Alice’s sister’s boyfriend. Hope that’s not too confusing! Since they met, BF and Dave have been inseparable. They’ve both been through some tough times together and they are genuinely like brothers.
Alice hates my boyfriend. Completely hates him and by default she dislikes me too. The first time I met her she said the only reason my BF is with me is because he likes “slutty girlsâ€. And that was the kindest thing she said to me that night. The second time we met was just as awful but I always take the higher ground and just pretend that I think she’s joking and laugh awkwardly.
Throughout the years, my BF has been disinvited to every single one of Dave’s birthday parties because Alice has expressed that she was uncomfortable (despite being married with a son, and another on the way) but we never thought she would go this far. When Dave mentioned to her that BF would be the best man she said she wouldn’t allow that. What’s hurting my boyfriend the most is that Dave just seemed to accept it.
My heart is so broken for him. He expressed to me that he doesn’t know why she hates him this much but he just wants Dave to be happy so he doesn’t want to cause a fuss by telling him he’s hurt. But I’m getting sick and tired of this grown woman dictating over Dave and my BFs friendship.
Another thing I’m worried about is her once again not being to help herself from making mean comments at the wedding and it upsetting me. The wedding will be 2 weeks after she’s given birth by C-section and the first time she will be drinking in a long time.
Does anyone have any advice as to what the best way to proceed is?
TL;DR My boyfriend’s best friend has said he isn’t allowed to be best man anymore because his future SIL (and BFs ex) has banned it.


Source.