Although I have a feeling he still would have called your bets (sounds like low stakes) I think you should have bet again on the turn.

While you may supsect he got the flush (I don't know why) you should still bet because I'm pretty sure you weren't 100% he was chasing the flush and you want him to pay for chasing a flush draw he may have caught on the turn.

also, min. bets in NL are pointless.