first I think it was a mistake to bet the Qx with that flop, but you did, so now that you hit the set what do you do
I might be wrong but I put him on AK or JJ , he might try to make a move to steal anyway I would call and try to see a showdown , I don't think I could let it go
Hope t see the result and you with a double stack

He's got middle pair and the nut flush draw on the flop so I definetely think a bet is in order, maybe a check/raise instead but I wouldn't want to fold or check/call out of position on that flop.

Results!

On the turn, I ended up calling and then checked the river. My opponent bet $600 and I folded. I should have just folded on the turn.

I think Stoneburg brings up a very good point here - there really is no reason for him to bluff at this pot, as it was unraised and I led twice. Why make this move now? He has a good size stack and is winning - he wasn't forcing the action before now - makes a bluff less likely.

D