When you bet the river, what will he call with that's worse than your hand?
If there isn't a reasonable probability that he'll call with worse, then why bet? If he's folding, you were pretty likely to win at showdown anyway, and you win the same size pot whether you bet or check behind. And if his calling range has a low proportion of hands you beat, you lose more when you bet and he calls than when you check behind. So betting is very likely -EV.
The other possible reason to bet is to get a better hand to fold. Since you bet a bit under half pot, he has to fold about 35% of the times he has a better hand for you to break even. Plus there's some chance you'll walk into a check-raise that you probably don't want to call but might feel obliged to since you already put in half your stack. Bleh.
But you shouldn't get to the river anyway. The straightforward action is to fold pre-. Since you called instead, it's easy to understand continuing after flopping TPGK in position. But most 2nl players aren't barreling the turn with a worse hand, so absent any contradictory reads, I fold to his turn bet.