I bought this book many years ago and have purchased it as gifts for all sorts of people. Friends, family, acquaintances--anyone who was having issues with partners, kids, parents, etc. This book is full of tools to better understand the person you seek to better your relationship with, and perhaps also to better your own understanding of yourself.
The Five Love Languages sets up 5 different ways that people give and receive love. We all appreciate all 5 of these languages, but usually we speak loudest in one or two of them (mine are physical touch and quality time). If we can understand the languages that our partner speaks, then we can better "speak" our love to them. This is not a book for you to "listen" better, it is one to help you "speak" better. Sure, it helps you to understand your partner's language, and maybe appreciate that they are showing you love when they wash the car (acts of service), but it is more about YOU learning to perform acts of service for your partner, because that is the language that he/she speaks. It also teaches your partner to "speak" YOUR language to you. If your partner is an "acts of service" guy, but you are a "physical touch" girl, he needs to learn how to show you he loves YOU by touching you--because that's what you speak.)
There are other books that go with this (like one for Teens) that are incredibly helpful, too.
I highly recommend all of the Love Language books in the series. You can't lose!