The biggest red flag for me in your post (and probably to others here as well) is basically the ultimatum of deal with what he wants or leave the relationship. Whether he loves you more or in a way he doesn't love anyone else is irrelevant to the fact that you have let him know you are not comfortable with his proposition...any person who is willing to give up their relationship for some young piece of ass isn't the kind of person I would want to be in a relationship with.
You don't state your ages or the potential playmate's age...but if something makes you uncomfortable first of all you should be able to express that (so should he). On the flip side, when raising an objection how does he act? I mean, you haven't posted a huge amount of detail...but if he reacts like a petulant teenager whose mommy is putting a damper on their good time...that's just not the adult way to handle things.
Please register! Welcome to the board. There is some very good info here, hope you stick around!
