20NL equivalent 6-max cash.

Hero is on BTN with Qc9c. Effective stacks are 125BB. CO is somewhat loose aggressive.,

Preflop: CO limps, Hero raises to 4BB, SB calls, CO calls.

Flop is KcJc4s. SB check, CO donks 6BB, Hero calls, SB folds.

Turn is 8h CO checks, Hero bets 18BB, CO calls.

River is 7h. CO donks 14BB, Hero raises to 48BB, CO calls.

CO wins with 7c4c.

I think preflop is fine.

Flop is good for my range. After CO's donk,. I didn't want to raise because SB could have a hand, so I just called in position. SB folded, so we're heads up.

Turn, CO checks, so I probe, representing a King. He calls. At this point, I assign him a range of second pair and worse, and some draws.

River donk confused me. The 7h doesn't interact with the board at all (I guess 56 got there, but that's all), and his sizing is very weird (14 BB into a 61BB pot). I thought that he had some marginal hand and wanted to showdown cheaply. After some thought, I decided to raise him as a bluff, trying to get him away from a marginal hand. Raise size is about 45% pot; maybe should've gone bigger -- he's getting 3.6 to 1.

I'm not sure my hand makes a good bluff candidate, since I block both flushes and straights, and some marginal hands like QJ and J9. Perhaps I should have just given up.

He showed 7c4c for a rivered two pair, which was unfortunate.

But what do you think of the line I took?