AJo in MP - bet scary river for value when checked to?

[dark_horse]

This is one of those damn hands where I'm not sure if I should bet for value on the river. I've tried to train myself to do it even when scared, and it in the long run it's been so far a profitable move at the 1/2 tables. But in this situation, I couldn't bring myself to bet. UTG bets into me on flop, I raise, he calls. Maybe he thought I was just playing position aggressor since I was the preflop raiser. The flop has two diamonds. On the turn he bets into me AGAIN. Is he trying to build the pot, does he want me to raise his monster? But I raise anyway, figuring my TPTK is good here. River comes an overcard and a 3rd diamond, and he checks. grr. What should I do? No read on player.

Party Poker 1/2 Hold'em (10 handed) converter

Preflop: Hero is MP1 with J[img]/images/graemlins/spade.gif[/img], A[img]/images/graemlins/club.gif[/img].
UTG calls, <font color="#666666">2 folds</font>, <font color="#CC3333">Hero raises</font>, <font color="#666666">3 folds</font>, Button calls, <font color="#666666">2 folds</font>, UTG calls.

Flop: (7.50 SB) 4[img]/images/graemlins/diamond.gif[/img], 5[img]/images/graemlins/heart.gif[/img], J[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(3 players)</font>
<font color="#CC3333">UTG bets</font>, <font color="#CC3333">Hero raises</font>, Button folds, UTG calls.

Turn: (5.75 BB) 7[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">UTG bets</font>, <font color="#CC3333">Hero raises</font>, UTG calls.

River: (9.75 BB) K[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players)</font>
UTG checks, Hero checks.

Final Pot: 9.75 BB