Preflop
Its fine to defend 43s to a 2,5X open.
Flop
Not sure why you are check-calling here? You basically have the nut low, and you only flopped a BDFD, which is not a lot to continue with. Yes he used small sizing, but a hand this bad is still an easy fold.
Turn
You picked up a flushdraw, so as played you can call any reasonable bet, but he checks back.
River
You have no showdown value, so your hand is definitely a candidate to bluff. However when he bet flop, check back turn a decent part of his range is going to be A high, which just improved to top pair. So I dont think, this is a good
bluffing card for you, and at 2NL I would probably use a very unbalanced approach and only bet the river for value in a situation like this. And if you had folded on the flop, you would not be here in the first place, so it kind of dont even matter.