What does it mean when a guy always asks to meet your dad?

He is trying to show you that he has honorable intentions. He also feels that if he gets dads seal of approval it would make you like/love him even more. Most guys would shudder at the thought of meeting a girls dad if all they had in mind was to just have sex with the girl.

A dad would instantly pick up on that. Actually if he did meet your dad and somehow your father rejected him, he would probably stop seeing you out of embarasment.

If you have been together for a long long time he may be asking him for permission to do something. I doubt that is the case if he has never met him before.

I think mainly he just wants to show he cares about you by meeting your family and getting to know them better. Basically building a relationship with your family to strengthen his relationship with you.