AITA for walking out of my sister's wedding after discovering my husband slept with my soon-to-be sister-in-law?

it. This is a tough one. I'm in serious need of perspective and advice here. So, here's the situation:

My sister got married last weekend, and it was supposed to be a beautiful day filled with love and celebration.

Instead, it turned into an absolute nightmare for me.

During the reception, I (20 F) was sitting at a table with my husband (29 M), "Jake," my brother(28 M), and his fiancée, "Megan" (soon to be my sister-in-law, 30 F).

We were all laughing, joking, and having a good time.

Everything seemed perfect.As the night went on, I noticed Jake and Megan exchanging these weird glances.

At first, I thought I was just being paranoid, but then I overheard a conversation between them that completely shattered me. They were reminiscing about a "wild night" they had years ago, long before either of them was with my brother or me.I felt sick. I pulled Jake aside and confronted him about what I heard. He admitted that he had a one-night stand with Megan years ago when they were both single. He swore it meant nothing and happened before we even met, but I was furious.

The betrayal I felt was overwhelming, especially since Megan was about to become a part of my family.I didn't know what to do. I was angry at both of them for keeping this from me and hurt that they were acting so nonchalant about it. In a fit of rage and feeling completely humiliated, I decided to leave the wedding without telling anyone.Now, I'm getting backlash from my family. They say I overreacted and ruined my sister's wedding day by making a scene. They argue that it was a past mistake, and I should let it go for the sake of family harmony. But I can't shake the feeling of betrayal, and I don't know how to face Megan or even my husband right now.

So, Reddit, AITA for leaving my sister's wedding and not being able to let this go? Should I have stayed and tried to keep it together for the sake of my sister's big day, or was my reaction justified given the circumstances?

TL;DR: Found out at my sister's wedding that my husband had a one-night stand with my soon-to-be sister-in-law years ago. Left the wedding in anger and now facing backlash from my family. AITA?