However happy we may ever be with our partner, our love for them necessarily prevents us [unless we live in a polygamous society] from starting other romantic liaisons. But why should this constrain us if we truly loved them? Why should we feel this as a loss unless our love for them has already begun to wance? The answer perhaps lies in the uncomfortable thought that in resolving our need to love, we may not always succeed in resolving our need to long.
(Alain de Botton - Essays in love)