Affairs of the heart
Ben at Marriages Restored has a great series of posts warning against the damage an emotional affair can do to a marriage. Go there and read part 1, part 2, and part 3. When Mrs. Happy and I were engaged, she told me that she felt good to be marrying a man incapable of adultery. I said, "But I thought you agreed to marry me!" I told her that I'm quite capable of committing adultery, and that the more I'm aware of my weaknesses, the more I can compensate for them, thereby lessening the chances of succumbing to temptation. Better men than I (King David, for example) have committed adultery, so it would be arrogant of me to think that I'm immune to that sin. We discussed that for several hours. She couldn't imagine me as an adulterer, but I knew that the moment I think I have any sin under control is the same moment in which I drop my guard and open myself up to failure.
We brought it up in premarital counseling, and our counselor confirmed that every man is capable of adultery and that every good man is constantly on guard against it. Women aren't immune to the temptation either. Ben's story shows that sex outside of marriage is only one of several ways to commit adultery. It's important to guard your body, your mind, your heart, and your spirit. The parts of your life that you leave unguarded are by definition the parts most vulnerable to attack.
