A friend and I did some things... and now I need advise!

sorry if this is in the wrong subforum!

Righty, last Saturday I stayed over at my friend's halls and we watched Harry Potter at the neighbouring flat with some people I know too. When we started watching the second one, my friend went to bed and eventually all the other people with us did too, except for one guy, whom we shall refer to as C.
I was lying on the beanbag on the floor and he was sitting on the couch. When the girl who'd sat next to him had left, he asked me to come sit on the couch and he told me I could lie my legs on his lap, like we had done before sometimes. So I came over, sat down and then he insisted I'd get under the duvet too.
Basically, what happened next was very surprising to me. C started stroking my legs in a, for me anyway, very arousing way. He did this throughout the film and somehow I ended up stroking his neck. It felt really good. At one point I remember him saying something about taking me to his room and keeping me his dirty little secret, but I don't remember the context of it.
When the film had ended he asked we where I was going to sleep. He suggested I'd take his bed and he'd sleep on the floor, or we'd both sleep in his bed (as I protested against him sleeping on the floor), but in the end I went back to my friend's flat to sleep on the couch as was the original the plan (my main reason for this was because I didn't want to face C's flatmates in the morning and think we'd had sex).

Because the thing is, he has a girlfriend and he's been with her for seven years.

Since this happened I haven't really found myself able to let it go. I'm not sure what to think, feel or do. I feel like in a way I'm blowing this all out of proportion by spending so much time thinking about it, but on the other hand I also keep finding myself pining for more and hoping, I don't know, that he'd do something (sorry for being vague, I'm not entirely sure what it is I yearn for). I've even started writing something that resembles a diary and I'm spending time trying to find songs that fit my mood.


I don't really feel comfortable with telling any of my friends, 'cause most of them know C. I suppose what I'm asking is; what would you do in this situation?
Or just, if you have any words of advise on how to let go, or the situation in general, it'd be much appreciated.


ps. kudos if you read all of that!

At one point I remember him saying something about taking me to his room and keeping me his dirty little secret, but I don't remember the context of it.