To show gratitude is to show that we can be touched by human gesture. Once you can no longer be touched but have to be impressed, you've set your standards too high. Don't kill - the sixth commandment. It's not about getting a knife and cutting someone's heart out. You kill primarily with words, by crushing someone's spirit and individuality, trying to shape people according to your own desires.
Rejection is the ultimate form of death.
This is not just about cheating in a relationship, but about abusing sexuality. It's a challenge to insure that our sexuality retains its mystery. It's orderly and gives you something to look forward to. When you go out of order, you don't know whether you're lovers or strangers. And it usually results in women putting more pressure on guys to commit, which leads them to bolt.