Preflop: this raise sizing seems a bit small for pre-ante according to most regs, but if you have a reason, go for it.

Flop: His large donkbet makes me think he would do this with value hands that are afraid of the flush plus some number of bluffs.  I doubt most players would do this with sets, plus QQ and JJ probably three-bet preflop.  I think he's more likely to check/call with a Q or a J unless he has AQ, but that again might three-bet pre, so I would put him only QJ, some chance of AQ or 66, and some bluffs.  Whichdrawing hands he chooses to donkbet vs. check/call, check/raise, or check/fold is hard to say given you have no reads.  Lower two-pairs are possible as well, though it would be pretty unlikely for him to call preflop.  With K,Q, and J of diamonds accounted for he doesn't have a lot of flush draws, and the most of the ones he does have either have ace outs of straight outs (T9,98), so you aren't far ahead.  I still probably call a bet here as I'm definitely in the toppish part of my range, but I would be very wary here.

Turn: This enormous bet allows us to fold a lot of my range.  I think our calling range should be pair/flush draws, QJ, and 66.  I think we can shove for value with JJ and QQ, and bluff-shove with straight+flush draws.  I like folding KQ no flush draw here.

River: As played, I would definitely fold the river.  KQ has got to be the bottom of your turn calling range, right?  You aren't calling with QT are you? This is a pot-sized shove and it's optimal to fold about half our range here.

Results:  Is this correct?  Your post title says you lost, but the HH shows him with KhTh for a busted draw.  I will assume the HH is correct.

I'm a bit surprised to see him show up with a hand that wasn't a flush draw on the flop, but an open-ender with a backdoor flush draw is a decent semi-bluffing hand.  I think it's probably better as a check/call hand to give him some excellent bluff check-raises on the turn if a heart comes.  I think he played the turn and river perfectly.