The Good Marriage by Judith Wallerstein and Sandra Blakeslee is really good, A Happy Marriage, by Rafael Yglesias. Another great read is Secrets of a Happy Marriage by Angela Watkins Thomas and I'm currently reading Communication: Key to your marriage by H.Norman Wright. Other good books for sex and intimacy include; Sexual Intimacy In Marriage by William Cutrer and Sandra Glahn, which I have to say has to be my next reading material, as I have seen from reviews that it has good pointers for my marriage.
The Bible has more reliable things to say about true love than any other source. God being love incarnate, and being the One who instituted marriage, love and relationships in the first place, is definitely the Authority on this subject. Song of Solomon paints a pretty vivid picture of marital love; I Corinthians 13 spells out in detail the qualifications of love. There are so many more: it speaks separately of Phileo (brotherly or familial love), Eros (sexual love) and Agape (Divine love). I've been happily married for 13 years: the Bible works.