I don't want to gatekeep but I had no idea you could be "straight" and "demisexual" at the same time. Demisexual are people for whom primary characteristics (such as body) is not important, they are more about the relationship and emotional connection.
I also fail to understand your conversation with your friend. You have sex with him and enjoy it. You are friends, thus, there is some emotional connection. You are demisexual. Are you attracted to him or not? So confusing.