Thanks for the advice guys, and yes kml I too feel that he is a suicide risk.
I think for now, I can be his friend, but should not be intimate (of course, that could risk my health if he is not in his right mind and being careful) and just be there to listen.
I can start to not pursue, but be here for him if he needs an ear or something... . . .
I do think I should put up a wall to protect myself.. and to keep my self respect... but I think perhaps the friend approach would be a good path to follow for now. I mean, I have been his best friend since he was 15 years old... he really doesn't have anyone else right now.
I disagree (that's what makes this site so great -- you can get opposing views, and do what YOU think is best for your sitch ), but if you DO go this route, I'd strongly encourage you that all topics are open for conversation except OW. It is incredibly direspectful to you and to your marriage for him to just talk to you about his affair partner, when he is still married to you. And it's NOT good for your self-esteem and strength, either.