Caught In A Kink Experiment With My Brother-In-Law

I’ve been married for five years now. We have two kids under the age of four, and I’m a stay-at-home parent. My husband’s brother, let’s call him Mark, came to visit last week. He’s in his early thirties, about six or seven years older than me. From day one, there was just something different between us. It felt like it went beyond being friendly siblings-in-law. On the second night of his stay, we were all at home and my husband left to grab dinner for everyone. Mark and I ended up alone in the living room talking about old times. The atmosphere shifted from normal conversation to flirtatious banter pretty quickly. He made a comment that hinted towards us having similar interests or fantasies. I think he was testing me, seeing if I’d react like him. That night when my husband returned with dinner, Mark had already left for his hotel room down the street. But the seed was planted, and we both knew it. A few days later, after dropping off the kids at a family friend’s house who were babysitting, Mark sent me an instant message asking if I wanted to talk again about those fantasies we both hinted at last week. I thought long and hard about it that evening when my husband was asleep. It was wrong in so many ways, but it also felt right because of the sexual tension between us. We decided on a safe word and agreed this would be consensual roleplay only for one night. That night came, and we met at an Airbnb place far from town. I had never done anything like this before with someone outside my marriage, and while it was incredibly intimate and erotic, there were also moments of guilt and fear. Yet the sexual chemistry between us was undeniable; every touch felt electrically charged. We decided to keep our experiment a secret, especially since he’s related to my husband. After that night, Mark went back home, but we agreed to check in with each other from time to time. I’m still figuring out how this will affect my marriage and relationship with him going forward.