From Marriage and Morals

The essence of a good marriage is respect for each other's personality combined with that deep intimacy, physical, mental and spiritual, which makes a serious love between a man and woman the most fructifying for all human experiences. Such love, like everything that is great and precious, demands its own morality, and frequently entails a sacrific of the less to the greater; but such sacrifice must be voluntary, for where it is not, it will destroy the very basis of the love for the sake of which it is made.

--Bertrand Russell