Preflop
I would also take a free flop.
Flop
I would also check back. You have decent showdown value with second pair bad kicker, your hand dont need much protection, and its not good enough to go after 3 streets of value.
Turn
Here I would also bet two pair obviously. Now the hand gets interesting, because not only does he check-raise, but its an overbet of 2X the size of the pot. It would be an absurd
bluffing line, because he depend on you betting, and then he is risking 11,6 to win 3,6, which mean, this need to work 75% of the time.
So I actually think, you are likely to be beat here, and I would not hate to simply fold now and get away cheaply. A7 and 77 are hands, that improved on the turn, and could make sense to play this way for value. Or maybe he has pocket aces and was hoping to get a chance to check-raise you either preflop or on the flop, which you denied him by not betting. So now he is trying to make up for lost value by overbetting.
River
Flush draw came in and he still jam, which is an even larger overbet of 3-4 times the size of the pot. It can be argued, if sets or two pair take this sizing on a flush completing card, and if not, then he is only representing a flush, which is unlikely to play the flop and turn like this. So he is not representing much.
But at the same time its an absurd bluffing line, and there is an old saying "never go broke in a limped pot", which point to the fact, that the stack to pot ratio is just so deep. So as played I fold here and live to fight another day. I would rather give an unknown player credit for having a big hand, that he played in a weird way, that for making some wild
bluff, where he is risiking his whole stack to win a very small pot.