[bighead9]

I think you have to fold this one. If the guy is making a blind move with missed overcards, I think you fold, tap the table (so to speak) and move on - you aren't committed yet. If he has an overcard that is a diamond and he's therefore on a flush draw, you still lose about half the time. And of course, if he has a bigger pair or a flush, you're screwed. So it's a pretty easy fold I think, since most of the time even if he is bluffing, he is semi-bluffing where you still lose about half the time.