Love implies sacrifices. Making a sacrifice for someone you love is playing the cooperation card. A failure to make a sacrifice in return, a dishonesty or infidelity, is a defection. Sucker's payoffs in relationships include being left alone to raise the children while the ex-spouse goes off to marry someone younger.
The social trappings of love, such as the engagement ring, the wedding ring, the ceremony itself, are tangible manifestations of cooperation in the game. If I live with you, I want a ring within a certain period of time, may be translated as, if I play the cooperation card, how do I know that you will do the same?
Love is a game that only succeeds if both parties play every round in the cooperation zone. Marriage thrives in an atmosphere of perfect honesty and openness. Marriage is delightful when your spouse is someone you can tell anything to, discuss any problem or issue, without fear of betrayal. Jealousy implies a strong fear of defection. If you knew your spouse would play the cooperation card on every iteration, why would you ever be jealous? Jealousy can only be based on three things: an unsubstantiated lack of trust caused by your own insecurity, strong evidence that your spouse intends to defect at the first opportunity, or by a prior defection that has likely gone unpunished, because you are still there investing your energy in jealousy.
As in every other type of prisoner's dilemma, the shadow of the future is important. A marriage, which is supposed to be for life, is an endlessly iterated series in which any defection may provoke retaliation or end the relationship entirely. Most spouses have invested enough time, energy and emotion in forming the relationship that they fear this. A spouse who loves so profoundly yet so passively that no defection will ever be punished gives the other an incentive to defect, as the future has no shadow. Some defecting spouses avoid the problem through denial, convincing themselves that a defection doesn't count if it is not discovered.
The tit-for-tat strategy, so successful in stabilizing the game and causing cooperation, is widely adopted yet officially disfavored in relationships. In a James Thurber story I remember from childhood, a woman who could not bear a stupid story her husband told at parties finally retaliated by always telling one of her own. If you never wash a dish, my most effective answer may be to stop doing so myself. If it makes you sick to be surrounded by dirty dishes, you will end up pitching in. Yet the official view on tit-for-tat is that it is petty, and not worthy of love, but detracts from it. Love is supposed to be unconditional and selfless, inviting the sucker's payoff. When I was spending a lot of time reading my wife's manuscripts but having trouble getting her to read mine, I threatened to stop (an instinctive reaction long before I had read anything about the prisoner's dilemma). She was shocked that I would link the two issues. Any sentence in a lover's discussion that begins, "If you really loved me...." certainly deals with the outcome of a prisoner's dilemma or preparations for the next round: if you really loved me, you would cooperate is the innocent version; if you really loved me, you would continue cooperating despite my defections is the vicious version.
Tolstoy pointed out in "Family Happiness" and many others have also perceived that there is a serious distinction between being in love and loving. Being in love is the first rush of strong emotion when the game is about to begun. At this point the only cooperation desired from the other is to be there. Being in love is effectively a relationship you have with yourself that is catalyzed by the presence, frequently dimly perceived, of another. It is possible, even quite likely, that you will fall in love with little or no knowledge of the other. When the smoke clears, and the issues become living together, finding a middle ground, mediating career interests and geographical issues, marriage, and children, the game has begun. At this point you begin to discover if the other is a cooperator or a defector. Love is the stage that can only be based on a series of cooperations significant enough to inspire trust.
If you lie to your spouse, you are a defector. The defection may never be punished if it is not discovered, but it is a defection nonetheless in the same sense that "getting away" with a crime does not mean you are not a criminal. One of the many sick elements in our culture is the constant encouragement of defection in relationships. For every Fatal Attraction which claims that infidelity may result in destruction there are a dozen movies which express the same message as Bridges of Madison County: a little careful infidelity, never discovered, can invigorate a humdrum life.
I find that mutual cooperation in marriage, and in other areas such as business, brings on a satisfaction almost chemical in intensity, a kind of high. When I look around and say that I am playing the cooperation card endlessly with others who are playing it with me, wife, family, coworkers, I am happy. I can look everyone in the eye, and need not be afraid to turn my back on anyone.
When marriage breaks down, its prisoner's dilemma element becomes more overt. Custody and support issues are a particularly painful and destructive manifestation. For some reason, there are many fathers out there who wish to see their children but not to support them. The law has intervened to unbalance the game by decreeing in most places that when the man withholds support, the woman cannot retaliate in the only way easily available, by withholding visitation. In any event, the children are likely to become pawns in everyone's game. "If you realy loved me..." becomes, "if you really loved the kids, you'd cooperate endlessly, despite all my defections."
All my life, I have thought that there should be nothing easier than for a man and woman to love each other honestly and peacefully, yet in practice this turns out to be so difficult, like all human activities. There is an entropy, a destructive force born of selfishness and distrust, which leads to defections in marriage as it does in all other zones of our affairs. Yet cooperation in love solves or helps solve so many other human problems, such as crime, drug abuse, welfare dependency and homelessness. As I have said elsewhere, all problems are best solved upstream, and all rivers begin in the human heart.