AK top pair fold for one bet?

[tl65\]

party 30/60

SB is 37/15/1.2, BB is 29/11/1.3

I raise AKo from MP, both blinds call

flop K9x two diamonds

BB bets, i raise, SB has the 'call any' button checked, BB calls

turn another blank

checked to me, i bet, both call

river T [img]/images/graemlins/diamond.gif[/img]

sb bets, BB folds.....

usually, i'd make the crying call, but i cant really see Sb instacalling anything on the flop that i beat when he bets into two people on the river......