Sure, it's possible he hit a set on the flop. Whatever the case, you were the ant under his foot, the dingleberry on his TP.

You've got to be the one forcing people out of the pot. Especially preflop. When he puts out that weak turn bet, you've got to think about the fact that calling the weak turn bet sends the message that you don't really have a huge hand - setting youself up for facing a huge river bet. It's possible he's just got A8, or a missed flush draw and is feeding off your fear. Find out where you stand and make him be the one to sweat.