boyfriend having sexual turn on of being in secret relationships?

So my bf just admitted to me he has a sexual turn on of being in secret relationships at least once a year. He has fake relationships. He doesn't love them or anything. It's purely a sexual turn on. I have a turn on by my bf having sex with someone else. I figure we match good cause of that. I didn't find much on the internet about it and wanted to know more about it. Apparently I started as a secret relationship but then he really fell in love with me deeply for real and I met his family a while ago for the first time and everyone important to him and we're in a long term relationship and living together. I just want to know if it's a healthy turn on to have? And just more information about it. I know people will think it's cheating but if I know about it and agree to it then it's fine.