<human>: About a month ago I went on a few dates with a guy I've known for a while. We hadn't seen each other for a while, and at that time he had a girlfriend, but it was over a year before. It was my impression that we were meeting as friends but as the first night went on it felt more like a date. When we parted we made out. I didn't know if he was still dating this girl but after that happened I assumed he wasn't. 

On our third date he stayed over at my place and we had sex. He left early the next morning and I didn't hear from him again after that.

Though we did get along, I didn't feel any romantic attraction to him, so when he didn't call me back it didn't really bother me. I was down with just a fun fling.

However, today while hanging out with a mutual friend I saw that this guy was still dating that girl and I found out because she had posted a picture of the dozen roses and poem he wrote her for Valentine's day. 

I don't feel hurt by this, but I do feel uncomfortable to be put in the position of the other woman. I think it's really unfair not only to his girlfriend but also to me. Right now I'm trying to debate if I should text him and call him out. If I did I would only say that I'm not trying to tell her and break them up but just that I know and that it was a shitty thing to do.

But maybe I should just do nothing! Especially since I don't feel personally offended by it.

Thoughts? What would you do?

Provide a brief overview of the text.
<bot>: Guy cheated on his girlfriend with me. I'm not hurt by it but am trying to decide if I should express to him how shitty his actions were.