[Pot-A]

Raise the flop. You're flush isn't very big, so you want to knock out the unsuited high diamonds if you can. Raise and pray for a reraise from UTG.

On the turn you have have to raise MP's bet. I think you're ahead often enough here that you need to try to extract extra bets from the lone big diamonds out there. If you raise the turn and get three bet by a player with even the most basic hand reading skills you're probably up against the nut flush. I've played with people against whom I'd fold and others I'd call, but either way you don't like your hand very much.

The decision that really got you into trouble here was the call before the flop. "How do I get the most for my nut flush?" is a much more enjoyable question to ponder than "could I possibly have the best hand?".