Playing sets vs flush draws
A standard problem situation I find myself in is the following.
Let's say I'm playing a fairly straight-forward, tight-ish FR game. I open raise 3x with 99 from MP and button calls, all others fold.
Flop comes 9J2, with two diamonds.
I bet 3/4 pot and he calls.
Turn comes another diamond... Do I bet here or just give up? There is just so little information about his holdings that I have no clue. If I do check, oop, I feel he more than likely will bet (either as a complete bluff after floating my cbet (representing the flush), or for value with the completed flush). I might call his turn-bet, but may have to give up to a big bet on the river.
Even if the turn hadn't shown a diamond, and I bet again, he calls, and the river shows the diamond... Do I just stop betting here? Obviously, I understand that I put massive pressure betting if the flush doesn't hit (in which case villain fold on river bet), but it does often enough for it to be a very big problem for me.
I find this very annoying and difficult. Obviously, in position this would all be a lot easier as I would likely donkbet or check-raise the flop, with decent bets trying to get my money in right there and then.