River decision

[tewall]

I'm sorry I don't remember more details, but I think it's enough to get some useful feedback from you guys.

I have K5 where the 5 is a diamond. The board has 4 diamonds, 2 on the flop. Also on the flop was a K, the high card for the board. The board also makes a straight possible (which was completed on the river). This is heads up. There is about T100 in the pot. I have T200 and my opponent twice what I have.

I misplayed the hand earlier to get into this mess, but what do I do now? I act first. My opponent is capable of calling without a diamond, and also folding (within limits, of course) a higher diamond.

I could give some information about my read, but it was all wrong, so I'll skip it. We'll just say I have no idea if he has a diamond or not.

Any thoughts?