My 2c for what it's worth to ya is:

Preflop - kind of a weak hand to play from UTG but in 6 max and if a fairly passive table not a bad limp. A more aggressive table I'd probably just fold it since I'd expect to be raised and this hand doesn't want to get raised - it wants to see a cheap flop, right? Preflop raise? - naaa limp or fold.

Flop - wow nice! 2 to a flush and 2nd pair - not bad! OK, you got ck-r so he's probably NOT on a flush or str8 draw.. Range of hands = TP, 2 pair. trips!

Turn - fantastic - a made flush. You're most likely well ahead. But you're ck-r again! Look at the board and re-examine the action so far. He just called pf so he wanted to see the flop as well. Ck-r on flop isn't someting a flush/str8 draw would consider logical so he's probably on the rainge of hand alread given. Turn - same action so most likely same range of hands and the board is not paired so a flush is well ahead of anything he's got. Maybe he's got you on a draw and is making it as expensive as possible although he should have slowed down with that 3rd diamond if he thought that!?! Right about here I would have gone all-in on my own!

River - good card. No pairs on board and villian isn't playing like he's on a bigger flush! I think he's in panic mode and is trying to bluff you off the pot - got to call when you have the best hand and it certainly seems that way to me!

So what did he turn over?

As I'm sure most can guess, I'd prefer 3 betting the flop.

Barring that, I think you need to shove the turn. If the board pairs on the river you'll be unhappy. If a diamond hits the river you'll be unhappy.

Pound the turn.

Based on stack sizes I might lead/3-bet all in.

I think you lose this quite often. I don't like it that you've repped a flush and he pushes the river anyway.

That said, your read of him says "donk and a half" so his range is far wider here than normal. Call.

He had ... meh

did i call that or what?

jon