AITA for refusing to attend my best friend’s wedding after she tried to steal my fiancé?

Okay, this might sound like something out of a soap opera, but I swear, it’s all true, and I need advice.

I (28F) have been best friends with Shelby (29F) for over 10 years. We met in college and hit it off right away. We have been inseparable ever since. Haven’t gone more than 3 days without hanging out. This is my sister soulmate. We’ve been through so much together… boyfriends, breakups, career changes, you name it. She’s been my absolute best friend, and I thought the world of her. I’m getting married to Ethan (29M) this summer in July, and I’m really excited, but here’s where things get messy.

Some months ago, Shelby and I were out for drinks, and we started talking about relationships (as we do). I’ve always been open with Shelby about Ethan and how much I love him. He’s honestly my other half, and we’ve been dating for 4 years, and we’re really solid. No issues. But out of literal nowhere, Shelby started asking weirdly personal questions about him… like details about our sex life, our future plans, how often we argue, etc. At first, I thought it was just typical curiosity or girl talk, so I answered her questions, thinking it was no big deal.

Then things started getting more uncomfortable. Shelby started slowly texting me a lot more about Ethan, asking about his plans, where he’d be, what he was up to, even things like "Does he like to do X on weekends?" It was so strange, but I brushed it off.

The bombshell came when I went on a weekend trip with Ethan to visit his family out of state. When we returned, I found out that Shelby had sent Ethan a very flirtatious text. He showed it to me, clearly uncomfortable but unsure how to handle it. She was commenting on how “handsome” he looked in a recent photo I posted, and how she was “thinking of him lately.” Ethan told me he immediately ignored it, but it still didn’t sit right with me. I decided to confront her about it.

When I asked her about the text, she became super defensive and claimed it was “just a joke” and that she “wasn’t trying anything.” She told me she was just “complimenting him” and insisted she had no bad intentions. At the time, I chose to believe her, but I was uneasy. This has never happened before. Never showed interest in Ethan over the years, I never even knew he was her type. So I brushed it off.

A few weeks later, Shelby invited me to a casual hangout at her place with multiple friends. I arrived, and I bring Ethan too. We are all taking shots, listening to music and playing drunken games. A few hours go by, I see Ethan walk back into the house looking uneasy and said he’d was smoking outside when he ran into Shelby and ended up having an “awkward conversation.” He said Shelby had been “very touchy” with him, asking him personal questions, talking about how “strong” he looked in a picture he posted on Instagram. He told me he was uncomfortable, but didn’t want to say anything to me in the moment because he didn’t want to hurt my feelings or make me emotional at the kickback.

Touching?? At this point, I was really furious, so I confronted Shelby the next morning. After hours of crying and multiple lies, she admitted that she had been developing small feelings for Ethan but claimed she never planned to act on them. She tried to gaslight me saying they were intrusive thoughts she couldn’t control. She apologized and said she was just going through some “emotional stuff” and wasn’t thinking straight. She told me she “loved me like a sister” and would never do anything to hurt me.

I was crushed. This wasn’t some small mistake; this was a betrayal of the highest order. My best friend, someone who I trusted with everything, my life almost, was harboring feelings for my fiancé and had been acting on them, whether she realized it or not. All this time. Was she plotting on me for years? That she could “steal my man”? How could I not see her being a snake? Shelby was always boy crazy, but never did I think she would ever try anything with Ethan. We are each other number 1 best friend, how could she think to do this to me?

I told her I needed some space from her. She begged me not to end our friendship over “something so small.” But I couldn’t shake the feeling of complete betrayal. I’ve always been the one who supported her through her struggles, but now I’m left questioning if she even respected our friendship in the first place. I don’t have many close friends, so I valued this friendship deeply. So deeply, I was naive enough to forgive her. We still text awkwardly, but it’s clear we aren’t as close. I don’t know why I’m still nice enough to keep holding on.

But here’s the kicker: She’s now getting married to someone else (someone she’s been dating on and off for years), and her wedding is in 8 months. She texted me a few weeks ago, asking me to be her Maid of Honor. I was floored. After everything that’s happened, she still expects me to stand by her on such a monumental day of her life, like nothing happened? Just forget it, right?

I told her I couldn’t do it. I finally said I couldn’t support someone who tried to sabotage my relationship. She called me “sensitive” and a “bad friend” and said I was “overreacting” and that she “would never do anything to intentionally hurt me.” Now she’s telling our collegiate mutual friends that I’m being selfish, and of course some of them are taking her side, saying I should forgive her and move on for the sake of our long friendship and friends like these aren’t easy to come by. But I just can’t. I’ve never felt so disrespected in my life. But I’m torn. No one cheated, so am I really overreacting?

AITA for refusing to be in her wedding and ending the friendship after everything that happened over what seemed so small and careless?