LMS, I had to respond to the advice, above, to "talk to him about his marriage and play therapist." Yes, this is one kind of affair that people can have. It's incredibly insulting to think that as a completely untrained therapist one could leap into a complex situation and "fix it," (and laughable that an affair partner could have enough distance to see anything except from his/her own pov), but some people do this to mitigate their guilt about interfering in a marriage. It is a way of bolstering low self-esteem and making themselves feel important when, obviously, they know nothing about making relationships work, or they wouldn't be there.
So far, I understand, you don't know whether this guy is married or not. If he is, do not expect to have these incredibly truthful talks with him, because if there's one thing men having affairs will be consistent about, it's about lying, lying, lying, and misrepresenting themselves and their situation. And who wants to be just another one of Tiger's--or any other version of him--conquests? It sounds as though you're looking for a lot more.
If you find out that this guy is married, there really is no reason for him chasing you which will lead to a satisfying relationship for you. 97% of relationships which begin as affairs fail because of the guilt and lies. I know you've already had various book suggestions, but I'd suggest looking at "Not Just Friends," by Shirley Glass. It has a section for the "other woman," explaining what traps she is falling into and how to turn things around so that she respects herself enough not to let herself fall for guys who aren't actually able to fully commit.
