If you love your wife, you won't have an affair. All marriages have problems, of course, so that can be one factor that contributes to infidelity, but it is almost always a combination of factors. I love my marriage. I have great sex at home. In fact, the sex outside isn't even as good, it's just different.
Sex is often a more prominent motivating factor when a man has an affair.
For women, it's often the emotional connection. So a woman having an affair is usually more of a threat to the marriage than the man having an affair. Close friends of the Clintons insist that they share a very deep love, a very deep connection and a very deep passion. This goes against everything we think because we think if you've got that, then you won't do anything like that. But professionals who work in depth with couples know that it's just not true.