[Maliant]

I would 3 bet the flop, if he calls fire again on non diamond turn, he most likely has draw is pretty heavy drawing board, could have 89 or diamonds, or whatever. Fire again on non-scary river card obviously. If turn is a diamond I check / call to see what he does on river and because you have 2nd nut flush obviously, if fires again on river I would fold non-diamond river, bet a diamond river and fold to raise because he most likely has A high flush anyways. If you get raised after leading out on turn again that's not a diamond, especially if its some card that completes straight on board I would bet and fold to a raise, he is not bluffing at this point and can beat your pair of kings.