[tardigrade]

Limping pf is marginal here. I think you could play these from CO or button in a soft game where you can count on getting paid off well when you hit, but it's too hard to play this early when you just pair up (as you saw).

In fixed limit, I'd always semi-bluff on the flop, since if a diamond comes on the turn, I'm getting good odds to draw into the flush. You aren't guaranteed that in NL, though.

On the flop, with the pair and backdoor flush draw in EP, I think you can reasonably choose to be the aggressor or not. If I opted for aggression, considering I'm betting out with a relatively weak hand, I'd want to put in a bigger bet, around 1x pot. I'm hoping for folds, and back off on the turn if I get a caller, since most hands that call that bet can beat me. (If another diamond came on the turn, I'd lead again with the same bet as on the flop to prevent the villain from sensing weakness and betting larger than my drawing odds.)

I think the way the hand worked out, you have managed to trap another marginal hand in the pot with you. He doesn't really love being there either, but he can't fold to those bets. Either push those bets up higher to eliminate other weak hands (and definitively let you know you're beat when they call) or approach the hand more passively (judo-style) and adapt your response to the action behind you.

My probable response to that flop in that position would be to check into the field. I call a reasonably small bet to see the turn. If I get a diamond, I bet out about 1/3 to 1/2 pot to discourage a bigger bet behind me. If I don't, when the initial bettor was late and the opening bet was small, then I drop a roughly pot-sized bet and try to win it on the spot if an overcard or other scare card comes. In the remaining case, I'll check-call a wimpy bet. And either check-call another wimpy bet on the river or check-raise about 1-2x the bet if I hit 2 pair.

I guess my play would be to try to simultaneously A) improve and trap, B) sense weakness and steal, C) avoid getting more than a couple BB involved in a prolonged marginal confrontation.