Well, I dunno about relationship books. Becoming less boring, though, there is one recommendation I have. Usually it's used to GET dates, not keep a relationship going, but it works very well inside relationships as well, and just in social situations in general. A program called "cocky comedy" by David DeAngelo. It will help you in social situations immensely, if you work through the program completely, and give you a greater understanding of how to, for lack of a better term, be "THE MAN" in any type of socializing - parties, dates, you name it. It's pretty effin sweet.
Here's the direct link to it. It's kind of expensive overall, but you pay in smaller monthly installments so it works out well for us working stiffs. Definitely with the monthly price tag. He also gives a 30-day no-questions-asked moneyback guarantee so there's not really any risk.
Jam it back in, in the dark.