Preflop
I am not a fan of min-raising in a cash game with deep stacks. The GTO sizing is likely 2,5BB, and if anything we want to size up in the micros, because people call far to much, and they dont 3-bet enough. 3BB was standard in
online poker for years, and I dont see any reason to not still use that size in a 2NL game.
Flop
Standard C-bet, and now the hand get interesting, because he check-raise. I dont think, there is any decision here other than call. Folding would be insanely nitty, but we also dont want to play for stacks this deep with just a one pair hand, so there is no point in 3-betting and reopening the betting for him.
Turn
Its not that likely, he has a flush, since you hold Ad in your hand, but KQ also got there, and he can have all 16 combos of that. Other draws on the flop were Q9 and 98, which you still beat. But for those hands the turn card was really bad, since you might now have a flush or straight, so those hands should probably just check and try to get to showdown.
Which mean, that when he does fire again, its really difficult to find logical bluffs in his range. I guess, he could be firing with QJ with Q of diamonds or KJ with K of diamonds, because he picked up draws and dont really know, how to play a combination of top pair and a draw. But apart from that I dont think, you ever have the best hand here.
I also dont think, you have great implied odds on the river, because on a 4-flush board a lot of hands are just going to give up. If for instance he has a straight, he is not going to put in a lot of money on the river, unless he specifically has the K or Q of diamonds. There are also some reverse implied odds, which the rabbit hunt illustrate. On an ace you improve to top two pair and might feel, your hand is now to strong to fold. But you still lose to a flush, straight or flopped set.
As others have said, there are also 3 combos of straight flushes, that have you drawing completely dead. So I dont think, this is an insane fold, but personally I would still call and see, what happen on the river. Sometimes he might slow down and check, and sometimes you will improve to the best hand. Folding here is a little nitty, but its not like, its the worst fold ever, when we look at the entire situation.