This is so dumb to write out yet is all true. Relevant history - Close to ten years ago my sisters MOH (Alison) and I dated for close to a year before I accidentally discovered she was closeted. The revelation allowed her to come out and she was accepted by everyone, yay for her. It was rough for me, while I handled it as best as could be expected it really messed with my head and ability to trust in dating, especially since the consensus was I should just be happy for her and it wasn't her fault. My sister remained close to her and I've done my best to ignore Alison's presence whenever we are in the same place.

LSS two weeks ago my ex (Eve) and I broke up after an on again/off again 2.5 year relationship. While we all went to the same college, my sister had never been friends with Eve prior and would not have if not for us dating. Sister is getting married and her bridal shower (which is mixed gender) is this weekend, she mentioned Eve had reached out to say how excited she was for it. After sitting on that for a day I asked her if she thought it was weird for Eve to be there and suggested that wasn't cool. My sister insisted that she had talked with Alison and that Alison said "We are all adults so we can deal" ...and I pretty much lost it. It's easy to say "We're all adults" when you aren't the one affected. I told my sister as much and asked her to choose, me or Eve. She said she chose me but didn't want to deal with this because "she couldn't uninvite Eve after she had been invited for so long". I told her in that case I'd be stepping down from her wedding party because if she didn't choose me I would treat her the same.

Sister was pissed at me for saying that keeping the peace was more important to her than my feelings, claimed it was her day and she "should be able to have her cake and eat it too". I told her that was the definition of impossible and that she was allowed to do what she liked, but that actions have consequences and to remember this choice was hers. Ultimately she did uninvite Eve, but not without painting me as a villain and announcing the situation to our entire family. Given I had to force her hand and she doesn't seem to care I still want to drop. AITAH?

Additional info: MOH is not Eve. My sister opened up the conversation about Eve still coming "as a warning" by saying that her and MOH decided everyone could be adults which set me off due to the history with MOH where "everyone acting like adults" meant she could stop using me as a beard while secretly dating a woman and I could just forget that I was lied to for a year until a text popped up on her Macbook while we were watching Netflix.

Edit 2: MOH = Alison, Recent ex of 2.5 years = Eve