One night stand with a guy in a relationship?

Okay, I went to a party recently and the guy hosting it asked my gay friend if he wanted to do stuff. He declined and referred him to me (not knowing he had a gf [I didn't know either]). He said I was cute and I found him cute as well. So we did stuff (not sex) and he told me he had a girlfriend and that he was "gonna dump her anyway". He's not dumped her and I don't know where I stand morally. Advice?Thanks! <3