Both of these talks are very enlightening.
Ester Perel gives a summary of her book Mating in Captivity, explains how in love we seek security but in romance we seek adventure. How do we achieve both in one partner? This is basically the theme of the story Anna Karenina, who struggles to be faithful to her loving husband or give is to her passionate lover.
Jenna McCarthy talks about some of the universal secrets of successful relationships.
This PBS documentary provides an interesting history of marriage.