Trying to understand my friend's motivations for cheating on his wife with prostitutes?

I have a friend who’s very successful, went to top schools, has a multimillion dollar house and a beautiful wife and children. I found out recently that he has been paying prostitutes to travel with him on business trips – a different prostitute each time. Even before he got married he used to sleep around a lot so overall this doesn’t surprise me too much. He has always lived on the outer edge of moral norms. It’s not that I’m concerned so much about the morality of this situation. It’s that I don’t understand the motivation. It seems to me that this is not about sex but I can’t tell for sure why he does it. Power? A need for excitement? Maybe he’s bored with his life? I really don’t know. Could anyone shed some light on this?