The book I would recommend that you read is "Love Must be Tough," by James Dobson. It's the best from the Christian perspective that you're seeking.
Beyond that, anything by Harley, Phil McGraw, Penny Tupy or Janis Spring is excellent, but you're going to need to read MWD's "Divorce Busting" or Divorce Remedy" (most think DR is a little bit better, and they're largely the same book), as many of the techniques you're going to read on this site ("180", "GAL," "LRT," etc., are from the books). I don't think that infidelity is particularly her strong suit, but you can apply the DB/DR principles in tandem with the affair-busting stuff, as I did.
