Well, that's good to hear, given that relationships with authority figures are never a good idea, for a bushel of reasons. The biggest problem you'll encounter is
the age factor -- I assume since he's a PhD and you're an undergrad sophomore that there's likely a 6-10 year age difference between the two of you.
I'm sure you're already aware of the special considerations involved in a relationship with such an age disparity, so I won't lecture. Really, as long as you know what you're potentially getting into and there are no authority issues to deal with, I can't see why you shouldn't give it a shot.