It's like the biggest BL nightmare. I was kind of in the same situation with my YF, but because his adoptive father really didn't care about him, I was finally allowed to just go ahead and be with him as much as I wanted. Which is just what I did. I guess your going to have to go by thier wishes, but I wouldn't actually "push" the boy away in any way. I think you could probably find a way to let him know that this is his Dad's wishes and that you would prefer to be with him. But also I would let him know that you feel you must abide by his father's wishes even though you might not want to.

Anyway, I hope this works out for you and your YF.

With Love in Christ,
Chris