Read the stories of other people on this forum who dated/married JWs. It just isn't going to work, is it? For one thing, if he is such a spiritual JW, why is he interested in you at all? He should be running the other way. So, a little lack of integrity there. And, later, when he decides he'd rather be a JW than be with you, it will all be your fault. I grew up JW, and so I know what I'm talking about when I say that JWs are screwed up in a major way and you are just asking for heartache.
Unless you don't want a future with him and just want to fool around. In that case, go for it. Why not?