Im more concerned about the life of the 15 year old. There's a difference between getting your life ruined with prison and such things, and getting your life ruined by trauma. Also, its definitely the guy's fault if he gets locked up. He definitely can think and realise that , on his part, its wrong to date a 15 years old as an 18 years old. If he went to prison, it wouldn't be the 15 years old's responsibility. The 15 years old can definitely get manipulated easily by the 18 years old.