Know when to Fold 'Em?

Here is one hand from last night that I’m really not sure about. Zendaten has been loose and very aggressive. He has been losing though and now a shortish stack.

Seat 3: zendaten ($10.35 in chips)
Seat 4: Phillberto01 ($38.60 in chips)
Seat 5: sonyc347 ($15.10 in chips)
Seat 6: Kokomo-Paco ($11.50 in chips)
sonyc347: posts small blind $0.10
Kokomo-Paco: posts big blind $0.25
*** HOLE CARDS ***
Dealt to Phillberto01 [Ah Ac]
zendaten: raises $2.25 to $2.50
A big raise. I’m thinking a genuinely big hand or AK or TT or JJ that he is worried about. Re-raise is the obvious play but I decide he may stack off if he has overcards or hits a pair given his aggression so I’ll let him do it.
Phillberto01: calls $2.50
sonyc347: folds
Kokomo-Paco: folds
*** FLOP *** [Qh Jc Th]
zendaten: checks
That is not a flop I like. I’m no longer comfortable about getting it all in. His check is also scary.
Phillberto01: checks
*** TURN *** [Qh Jc Th] [3h]
zendaten: checks
Well maybe he doesn’t have anything but I’m still suspicious. I have the Ah and a King and I have at least 6 outs and could well be ahead.
Phillberto01: checks
*** RIVER *** [Qh Jc Th 3h] [5d]
zendaten: checks
Ok a third check. Maybe he doesn’t have much. I opt to try and get something for AQ or a mid pair.
Phillberto01: bets $1.50
zendaten: raises $6.35 to $7.85 and is all-in
The Hammer. Not unexpected but should I just have checked it down. He is capable of making a play here given his earlier aggression but I doubt it. I’m thinking straight or trips here. But I also think KK could be a real possibility.
I beat: KK, a bluff
I lose to QQ, JJ, TT, AK.
joa34 joins the table at seat #2
I decide to let it go.
Phillberto01: folds
Uncalled bet ($6.35) returned to zendaten
zendaten collected $7.95 from pot

A reasonable fold?