Found on the net and I agree with it

A cuckold fetishist is aware of the spouse's activity and derives sexual pleasure from it. This knowledge and tolerance of the spouse's activities makes the person in such relationships a wittol, properly speaking. But among fetishists the pose of reluctance—the victimization of the cuckold—is a major element of the kink so the more familiar word is used. In the fetish cuckolding subculture, the female is typically sexually dominant, while the man takes on a submissive role, only becoming involved with her or her lover when she permits it—sometimes remaining altogether celibate. Other arrangements are certainly possible, however, as wives can have husbands who take female lovers with their full knowledge and approval but I don't think they should

The wife who enjoys cuckolding her husband is sometimes referred to as a hotwife or cuckoldress.

Theories in evolutionary psychology In his book Sperm Wars, biologist Robin Baker speculated that the excitement and stimulation of the cuckolding fetish emerges from the biology of sexuality and the effects of sexual arousal on the brain. According to his theory, when a man believes that his female mate may have been sexual with another man, the man mate is prompted by biological urges to copulate with the female, in an effort to "compete" with the other man's sperm. The effects of sperm competition are well documented. Further, when initiating sex, the man mate thrusts harder, deeper and longer, in efforts to remove the sperm of the other man and is biologically driven to have sex multiple times. While he may be unable to have sex more than once under usual circumstances, the cuckolded man is prone to repeated sexual efforts. Meanwhile, the wife enjoys greater sexual stimulation, first by her other lover and second by her cuckolded husband. In addition, the wife enjoys the neurochemical "highs" triggered by entering into a romantic or physical relationship with another lover. These highs include the effects of oxytocin, other neurochemicals which trigger excitement, euphoria and other feelings common to the beginnings of romantic relationships. The effect from this gives the female a natural high, which can offset the negative physical symptoms like body pain, headache, and anxiety. These neurochemicals change over time and as a relationship persists, with neurochemicals changing to ones that promote bonding, planning and nurturing. When a new lover is taken, it triggers the neurochemicals of a new relationship, bringing home excitement to her husband.

To end one relationship only to start another is a sexual high for the cuckoldress ,the cuckold ,and the new lover