Why would he do this?

tell him what you hink about the situation he got himself into no matter what you like him as he friend he is to you. Let him talk about what he is trying to get out all of this besides a lot of troubles..... if he is not married he at least shold break up wih the gf he is cheating upon maybe he is the sort of guy hat likes the feeling of getting caught so if he is single he might loose interest in the 16 yr old.......or try to scare him tell him there is talk and he doesnt want to go to jail right.......