I decided my son doesn't need to know anything!

I am a 56 Bisexual man in a friends with benefits relationship with a 22 year old man my son went to school with, they are not friends. I started this relationship and initiated it with this young man and after taking into account what people said, i decided to keep it away from my son unless he asks me, then I am going to tell him. As long as we are just casual with this young man, I think we don't need to be telling anyone.