Couple years ago, my best friend I grew up with since first grade were in college and we did a lot of partying and drugs. Went to a rave in Dallas, he met this girl. They did this long distance thing (like 3 hours away from each other) for about a year but had their issues.
One time she came up to where we lived and went to our college football game. His family has family tickets, so he went into the game with his family and me and her stayed outside and drank. We had a heart to heart and ended up making out. We never really spoke of it or talked to each other again while she went back home.
Fast forward a month or two, we go down to Dallas to see OU / Texas play. At this point, they were super rocky and considering breaking up. That night, we went out to a club. She didn't want to dance with him for some reason, but they were kind of fine other than that. We go outside for a cigarette, come back in and she's grinding on some dude. All hell breaks loose, they argue and end up breaking up once we're back at her house while I'm just sitting there smoking weed trying to watch a movie and eat.
We're all sleeping in different rooms at her house, and she comes into my room unexpectedly while I'm laying there. We end up having sex while we hear him snore in the room next to us.
We end up being "a thing," in secret for about a year. I'd make the trip down to see her every month, or she'd come up to see me when possible. No one knew but our parents. Her parents were totally cool with it too, they knew I was his best friend and I'm pretty sure they knew we were keeping it secret. They allowed me to stay at their house for days at a time. All we did was drink and do drugs, go to shows, party, and have lots and lots of sex.
After about a year, I'm down there seeing her, and one of our mutual friends finds out I'm going to a show and asks my friend why he's not with me since we always go together. He asks about it, and at that point, I told him I had been seeing her. He doesn't know everything, like me fucking her 30 minutes after they broke up and seeing her for an entire year and he never will, he just knows I had been seeing her the last few months because she was the only person I knew in that area when I went back home and that we were interested in each other. He pretty much gave me his blessing, so me and her became "official" and didn't have to hide it anymore.
We dated for another half a year, but I ended the relationship because she was moving further away to a different college and she definitely couldn't be trusted based on the shady shit she was throwing my way.
I didn't love the girl, but it was a fun time.
tldr: fucked my best friend's girlfriend 30 minutes after they broke up, saw her for a year without him knowing, confessed to only seeing her for 3 months and lied about anything sexual happening, gives me his blessing to date her, I break up with her because she was shady. Being 22 was fun.