AITA for refusing to attend my best friend’s wedding after finding out she lied about something huge?

I (28F) have been best friends with Megan (27F) for almost 15 years. We’ve been through everything together—good times and bad. We’ve supported each other through breakups, career changes, and everything in between. She was always there for me, and I was always there for her. At least, that’s what I thought.

A few months ago, Megan got engaged to Jason (29M). From the start, I was excited for her. She seemed so happy, and Jason seemed like a great guy. Everyone around me, including my family, loved him. They’d been together for two years before getting engaged, and I had seen how much they cared for each other. They were the picture-perfect couple in my eyes.

But everything changed when Megan told me something I wasn’t expecting. It started during a casual conversation at lunch. She mentioned how she had to cancel a girls' weekend getaway because Jason had a “work event” in town that weekend. At the time, I didn’t think much of it.

But then, the following week, my brother (who’s in the same social circle as Megan) casually mentioned that he had seen Jason out at a bar with another woman. He described the scene: they were holding hands, laughing, and it was clear they were very close. At first, I didn’t believe it. Jason was always so respectful and affectionate towards Megan. He was supposed to be committed to her. But the more I thought about it, the more I began to doubt. I asked my brother for more details, and he assured me that it was not a mistake—he had seen them together for an extended period and had even overheard part of their conversation.

I confronted Megan about it, but at first, she denied it completely. She seemed flustered and defensive, saying it was all a misunderstanding. She told me Jason was just helping a “friend” with something, and it was nothing more than that. But I could tell she wasn’t being truthful. Something in her tone gave it away. She was hiding something, and I couldn’t shake the feeling that she wasn’t being honest with me.

I gave her some space, but then a few days later, I found out some shocking news. Megan had been secretly talking to her ex—someone she had been in a long-term relationship with before Jason. They had reconnected through social media, and it turns out they had been messaging for months, even before Jason proposed to her.

I didn’t know what to do. Megan had always been an open book with me, so this revelation felt like a slap in the face. How could she lie to me like this, especially when it came to such an important part of her life—her engagement and future with Jason?

I couldn’t just ignore it. So, I confronted her again, and this time, she admitted everything. She had been talking to her ex on the side and, while she wasn’t planning to get back together with him, she had allowed herself to get emotionally involved. She also admitted that she had lied to Jason about meeting with her ex, and in doing so, she had created a web of lies that affected everyone around her, including me.

I was devastated. I never expected this from Megan, especially after all the years of friendship. I didn’t know how to feel. On one hand, I felt sorry for her—she had been so confused and caught up in her emotions. But on the other hand, I felt like I couldn’t trust her anymore. How could I stand by her when she had been so dishonest about something so important?

I told her that I couldn’t attend the wedding anymore. I told her that until she figured out her feelings and was honest with everyone involved, I couldn’t be part of it. She begged me to change my mind, but I stood firm in my decision. I couldn’t support a wedding built on lies and deception.

Now, Megan hasn’t spoken to me much, and I feel horrible. I know she’s hurt, and I know I might have made her feel abandoned. My family is split—some think I did the right thing by holding her accountable, while others think I should have kept quiet and supported her no matter what.

So, AITA for refusing to attend my best friend’s wedding after finding out she had lied about her relationship and her feelings for another man?