Yes, that happens. It can be one of many reasons, perhaps he’s just starting to explore who he may be and not ready to jump the fence. It can often be “experimentation.” Many of us have been there on the other side. Although from your perspective it seemed that he was totally “into it,” there are other factors that may have made the situation thrilling for him. Just because some of us have had sex with women and everything worked fine, and we might have even been “into it,” doesn’t mean we are necessarily “straight.” An all-new experience can be exciting. If he then tells you that he is not into dudes, DO NOT FORCE THE ISSUE. You have to take him for what he is telling you. Either he is not into dudes, or he needs to deal with his needs on his own terms. Going beyond the limits expressed by another guy could be construed as sexual harassment or sexual assault. Let go. There are plenty of other fish in the pond. Go fishing elsewhere.