Hi everyone. Recently I met a bi guy a bit older than myself. We had some very good sex, and afterwards he mentioned that he has a girlfriend. I asked him whether she knows about him seeing guys and he said no. This makes me feel a bit guilty, since I'm having sex with a guy that's already in a relationship without his partner knowing. I don't want to tell him how I really feel, however, since he's a cool guy and I enjoy spending time in his company (telling him might cause him to write me off). On the other hand, I can provide him with experiences that his girlfriend might not necessarily provide, since it sounds as though she is quite conservative sexually. What do I do in this case?