Should I have folded AA here?

[rodders133]

Full ring 5/10c
Folds to me in mid position, I have AcAh and raise to 40c,
SB calls,
Flop is 5d Kh Kc,
SB checks,
I bet 40c,
SB calls,
Turn is Qs,
SB checks,
I check,
River is 9d,
SB goes all in $6.36
I have $7.50 and fold.

A friend was watching me and said I should have called, and have since been doubting my decision.

I realised I showed weakness on the turn when I checked behind him so I suppose a bluff from him could be possible?