a strong raise against a strong hand

[cookperson]

I would like to bring up a certain type of hand that I always have alot of trouble with.I'm at a .50-$1.00 table with no read on villian. I'm in early position with $140 villian is at button with $155.I have a [img]/images/graemlins/spade.gif[/img]and k [img]/images/graemlins/club.gif[/img],preflop, and raise to $4. Late position and button call.The flop is a [img]/images/graemlins/heart.gif[/img],9 [img]/images/graemlins/diamond.gif[/img],and 4 [img]/images/graemlins/club.gif[/img]. Feeling pretty good about this flop I bet $13, late position goes out and villian calls.Pot is now about $41. Turn card is 2 [img]/images/graemlins/spade.gif[/img]. Now with a great board I lead out and bet $25 ,but much to my surprise button calls and goes all in. So now I have to put in $98 to see the river. My thought process is this: I know i have a great hand and a great board, but I have been showing strength by betting aggrssively on every street. Why would he suddenly re-raise me all in ? The board shown no flush or straight possibilities, so either he has the dreaded set, a hand similiar to mine or it is a bluff. My instincts tell me to fold, that he must have a set, but my head tells me to call. That i may have him beat now,and if not I can still catch a card that would give me the nuts.What is the proper move here, I run into this situation more times then I would like.