His Needs, Her Needs: a marriage that meets the emotional needs of a spouse is going to be more resistant to the temptation of an affair than one that doesn't. If your needs aren't being met in a relationship, you are going to be drawn to people who do meet those needs for you.
In my case the statement in green was not possible for me due to his NPD.
His needs will never be met due to what he lacks within himself to establish emotional intimacy. That's not just me..that's with anybody. Children, parents, siblings,friends ( which he has none), pets, anything.
He is devoid of feeling anything for anyone other than what he can manipulate or use to get a need satisfied without returning anything. We are all targets..marks...something to use and discard eventually.