"Many people need bursts of passion or lust. If their spouse accepts this, they may continue to be happy; if not, they might be driven apart and the cycle is repeated." [Warning: link leads to porn - TMR.]-- A businessman, in an article on adultery, in The Times Online.
"It can be fine for years, and then [they] actually fall in love, usually with a younger version of the [spouse]. That’s when trouble starts, and when I meet them, they are very angry.”-- Vanessa Lloyd Platt, a divorce lawyer, from the same article.