2nd nut low and double belly buster against a weak bettor

[TGoldman]

I prefer not to raise this one pre-flop. You certainly have a playable hand along with the button, so I don't think there's anything wrong with raising. Just be careful--you're going to find yourself in a lot of marginal situations trying to figure out how to best play with a 2nd nut hand for the low. Some players excel in those situations; Most struggle with them.

Calling the flop is okay since the price is right and there's a lot of cards you can pick up that either improve your hand or give you a backdoor draw.

Now that it's heads-up on the turn, I think you should at least consider semi-bluff raising, especially if you feel there's a chance villain might fold. The villain obviously doesn't like his hand very much, and he is probably just weak betting with some kind of draw. If he calls, you still have outs and can probably take a free showdown regardless if he is as passive as you say.