Regarding the question of if he's straight and just likes fucking guys or if he's bi, that's really up to him to decide. The wonderful thing about sexuality is that we get to define it for ourselves.
As to how to communicate what he wants from a potential sexual partner, it sounds like he has it pretty clearly figured out for himself already. Just putting it out there like you have here should do just fine. Being really specific about what you want helps to find those people who will fit well with you. (That doesn't mean it will be easy though, the more outside the box what we're looking for is the more difficult it can be to find those people who fit).
Everything will be ok in the end. If it's not ok it's not the end.