I think this guy is acting inappropriately. Since your connection to him was supposed to be professional and business related - he crossed the line in his emails and personal questions to you. He supposedly had connections you wanted - he's in the authoritative position. He figures if I scratch your back(giving you connections) then he'll take advantage of that and get what he wants. He's basically fishing and trying to sense if you'll bite and he's enjoying the chase.

I suggest you measure how valuable a connection he is - why do you have to be connected to him? If you're going to go out to dinner with him, you should have your own ride home - why the need for dinner?

How to handle advances like this - the humorous way is good but for me personally I like the direct approach. To me it's not worth it to get a few connections, but to have to deal with a married guy like this. I've been in sticky situations with married men before and I really detest men who are married being flirty. As Sabby said, you should trust your instincts. You can learn how to be assertive.

^^
I think the statement Byz gave, would be the perfect comeback for his question about casual sex lol.