NL5 Flopped Set, strange Preflop-Aggressor, push in spite of read?

[RoyalFarmer]

NL5 at Partypoker.

I have no stats or reads on my opponents. They seemed to be solid and didn't make any stupid moves.

All participants are fullstacks (5 Dollars).

Unfortunately I don't have the HH anymore, but I hope it's understandable.

UTG+1 raises to 0.16 (4x BB)

Everybody folds to me in middle position, I look at a pair of eights and call.
Everybody except the small blind folds, who calls as well.

Pot: 0.50 Dollars

Flop comes:

2d 8h Kh giving me mid-set.

Small blind donks 0.20, and the preflop-aggressor just calls. I raise to 0.6 (maybe too little).
Small blind calls and suddenly UTG raises to a total of 1 Dollar.
Pot is now 2,90.

At this point I felt like, woooow, how can UTG hold anything else than two Kings?! But I've flopped the second nuts, and that's exactly what I was looking for preflop.
So my question is, can I fold or do I have to push in spite of my read (who was really strong, instinctly)?

The only other hand I could put him on would be AA, but he would have played it really strange.

My english might be bad, since I'm a german. [img]/images/graemlins/wink.gif[/img]

Comments please.