Recently, I heard a book mentioned that sounded good, but I didn't catch the title. Basically, it's about whether or not this woman kissed this man, and how her life went if she did and how it went if she didn't. It doesn't tell you if she kissed him or not. Apparently it's written in two parallels, switching back and forth between how her life went either way. Anybody know the name of the book?

I think you are talking about "The Post Birthday World" by Lionel Shriver.