Fears that hold so still you can study them

I'm sitting in the big blind with five nine off and the guy in first position -- who happens to be the big stack -- comes in with a small raise and the table folds around to me. I call, figuring it's a cheap opportunity to build my table image as a player who gives action. What do you know, the flop comes five five seven rainbow and I'm looking at a set. I check and the big stack goes all in.

What's the right play? Well, he probably doesn't have a five which means that I don't have to worry about being out-kicked. So it's either a pure bluff, an open ended straight draw, or a pocket pair. Of all that, the only hand better than mine are pocket sevens. Of all the hands he might have, it's only with the straight draw that I'd consider making the bet he did. But that's my game and this guy has been over-betting strong hands and folding to raises all night. And, anyway, why would he raise pre-flop with six eight? So I put him on pocket sevens. And yet I make the call. And of course he's holding hockey sticks. As it happened, I sucked out a nine on the river to take the hand.

I'd like to be able to explain my call by saying that, in the long run, sticking to the principle of never folding a set will be a more successful strategy than sometimes folding. And that may even be right. But the honest truth is that I called because I just couldn't bring myself to let go of the best hand I'd seen in awhile.

Here's my question. Did I make a read on this guy or not? On the one hand, there's no denying that the little voice inside my head said that he was sitting on sevens. On the other hand, Aristotle assures me that if I'd really believed that he had the nut set then I would have folded.