First off, I agree with Ariakas, you have the right to know. Although the problems are not deal breakers for you personally, the lack of honesty should be. Don't put him on too high a pedestal just because he is "nice" and "sexy"
Second, researching is not stalking. The big difference is that you had concerns and you looked into it. Period. Final. Stalking would be continuing to gather more info, getting multiple credit reports or info reports, following him or his family, etc.
As for how to broach the subject, go ahead and be honest. Tell him that you did a search online out of curiosity and you wanted to be sure if what you found was him, and true. Then launch right into asking if he's married before he gets the chance to ask you what you found out. Kinda devioius but as we all know, it's harder to hide the truth when you think the questioner knows something.
Then if he lies, or disembles(sp) or jumps right into accusing you of invading his privacy, those should be deal breakers becuase he is hiding something, probably not just from you either.
Good luck either way.