I don't think that he's unfaithful to me, at least with that girl, because of two reasons. Firstly, they hardly know each other so their contact is at the "hello" level and secondly even though he likes her I don't think she likes him. She goes for guys of completely different type from him. He look to be unfaithful to you. Tagging any longer with him will only just waste your time. Some people, I have talked with suggested that for him to stay hard these long periods of time he's fantasizing having sex with her. What I want to know is whether this is the only possible explanation for his hardons and whether these fantasies are controlable (you can get the out of your head) or not.