I have another book recommendation that I heard of on another poly forum. I think it would be handy for any relationship that is struggling with communication at all, though due to it's nature probably best for heterosexual ones.
"How to Improve Your Marriage Without Talking About It: Finding Love Beyond Words" by Patricia Love and Steven Stosny.
I think if I had read it a few years ago it would've smoothed a lot of the road to our way back to re-opening our relationship. My husband actually read it without me asking it and found it helpful and accurate, which rarely happens, so I was extra impressed. I even feel like we are both a lot less prone to taking things personally since I got it a month ago, which has introduced a new layer of mellowness to our relationship that I really like.
Happiness will never come to those who fail to appreciate what they already have.