AITA for leaving my husband after I found out he was cheating with my sister-in-law?

I (33F) have been married to my husband, Adam (36M), for eight years. We met through friends, connected instantly, and got married two years later. We have a son, Oliver (6), and a daughter, Mia (4). Our life seemed perfect—loving, stable, and ordinary. Adam was attentive, supportive, and always seemed trustworthy.

His younger sister, Rachel (30F), has always been part of our family. I considered her a friend, almost like a sister myself. She helped with parties, babysitting, and often gave advice about parenting. At first, I never suspected anything could go wrong.

About a year ago, I noticed subtle changes. Adam started coming home late more frequently, leaving the kids with me and claiming he had extra work. Rachel also began spending more time at our home, sometimes staying late. I thought nothing of it—until small details started bothering me.

One evening, I returned home early from a work trip. I found Adam and Rachel in the living room, sitting unusually close, whispering and laughing in a way that didn’t feel innocent. My stomach sank. Something about their interaction seemed intimate and secretive.

I decided to investigate discreetly. Over the next few weeks, I discovered messages and emails on Adam’s phone showing months of flirtation with Rachel. They had been planning private meetups, sending affectionate texts, and even talking about future trips together—all while pretending to be part of our family.

I confronted Adam immediately. He initially denied everything, claiming it was harmless joking. But when I showed him the messages, he admitted to having an affair with Rachel for over six months. He claimed it was emotional at first and “just happened,” but he couldn’t resist.

I also confronted Rachel. She admitted to knowing he was married but claimed she didn’t mean for it to escalate. Her lack of remorse left me feeling betrayed and humiliated. My husband and his sister—two people I trusted completely—had destroyed my sense of security and trust.

The emotional impact was devastating. I couldn’t eat, sleep, or focus. Every memory of family gatherings, birthdays, and holidays felt tainted. I realized I couldn’t stay in a marriage where I couldn’t trust my husband or his sister.

After weeks of deliberation and seeking advice from friends and family, I asked Adam to leave and filed for divorce. Some people told me I should forgive him for the sake of the children, while others supported my decision, saying betrayal this deep is unforgivable.

Now, months later, I am rebuilding my life with Oliver and Mia, focusing on healing, work, and protecting my children’s emotional well-being. I am learning to trust myself again and create a life free from deception.

So, AITA for leaving my husband after I found out he was cheating with my sister-in-law?