This is tough because it is a scary board, so calling and letting another card peel off is gonna be rough. But folding two pair is really tough too because that could easily be the best hand.

You are crushed against KK, AQ, Q9, (also TT and JJ, which are very unlikely). You are beating KQ, AA, QT/QJ. As you said, you 3-bet him a couple times, and he could easily be doing this with any hand and be tired of you pushing him around.

I could see them doing the same thing with a flush draw (with the Q of clubs).

It's a tough call, because there are so many scary cards that can fall. Whether they are bluffing or have it, they are probably gonna continue and lead out on the turn, and you're basically faced with the same decision.

Definitvely, I don't know. I seemed to ramble a little bit and not help much haha. I think I would probably call and evaluate later (although that is probably a bad play).