Maid of honor with ex as best man

I was asked to be the maid of honor in one of my best friends' wedding! Should be exciting right? Well it was until I found out my ex is going to be the best man (the groom and I went to high school together and we're all friends with my ex years before I dated him). It was a horrible relationship to say the least. He was arrested for domestic assault while we dated, stole rent money, lied about him having a child, and even lied about having cancer. Both the bride and groom were there for it all. so when I was told he would be the best man I got extremely anxious. The wedding is in Puerto Rico so it's more like a week being spent with him, not to mention my current boyfriend has to spend with him. Now I find out that she wants to have both the bachelor and the bachelorette parties in NYC at the same time. I questioned having to walk down the aisle with him in the beginning, but she won't budge on not having the maid of honor and best man walk down the aisle together. She is now upset with me because I said I would go to NYC but just skip out on when the two parties meet up, mostly because I feel it's disrespectful to be there with my ex and not have my current boyfriend there. She has told me

I half agree with the above reply. I'd suggest talking to your friend again, remind her of your problematic relationship with your ex and point out the obvious potential problems of your ex and current boyfriend together = potential punch up when everyone's had a drink or three. She doesn't have to change her plans. She can accept that you, your ex and your current boyfriend will be adult and civilised during her special day and as much as possible before and after where you HAVE to be near each other. But she should surely accept that you can't participate in the before and after stuff that involves you or your boyfriend having to socialise with your ex. If she can't accept that then she's not really such a great friend after all and you could rethink your commitment to her as a bridesmaid.

I've tried twice now trying to explain my feelings but she said that it is "her wedding and she wants what she wants." I have thought that it's not fair to me or her at this point for me to be in it, but if she's this upset with me for saying how I feel then how do I try and decline from the wedding party and remain friends? We have all of the same girl friends and I don't want the dynamic of things to change