Threesome with my [M25] girlfriend and my side-piece [MFF] [CHEATING]

A few things: I know that this isn’t as wild as a lot of your guys’ stories, and I know that this is morally “wrong”, but that’s not why I’m here. Also, the title is slightly misleading, but not terribly so.
Here’s the story:

A few years ago, I was in a really bad long distance relationship. It was good for a while, but we both grew totally out of each other without actually cutting the cord. So one time near the latter portion of my terrible relationship, I was over one of my good lady friend’s houses. We had always had some really strange sexual tension between us, and before my relationship we had exchanged some dirty snaps a few times, but we had never done anything with each other…until today.

So, I was over my friend’s house, and she had been flirting and making some comments. She commented about how tight my pants were and she joked about how she thought she saw an outline of *something* through the pants. When she turned around to put a dish away, I came up behind her and started feeling her up. Ballsy, I know, but it worked out because she grinded her hips against my crotch. After some handsy stuff, I pulled down her tights and fucked her right over her kitchen counter in the middle of the day.