Sexual desire declines after four to seven years. That's been proven.Because it's the most compatible with our spiritual origins. Father, mother, small family - that's the way we've developed our souls, the way we've become, and the way we feel safe, protected and loved.
The sexual revolution produced cultural convulsions that were unparalleled in the 20th century. The female sex was historically sexualized and required to have orgasms for the first time. Sexual "deviants," particularly homosexuals, achieved partial emancipation.
With an intelligent couple, it ought to be possible for the husband or wife to look for satisfaction outside the relationship - while always taking the partner into consideration, meaning acting openly but still discreetly.