My theory: Logic weighs more in a decision by males than by females. Feelings weigh more in a decision by females than by males. Where a man evaluates things with logic as to what is to his benefit, a woman perceives what is to her benefit through feelings instead of logic. There is evaluation happening in both cases. A woman feeling she wants to be with a man or feeling love for a man has more factors influencing it than the love of a man because of this difference in logic versus emotional decision making. Those factors are 'conditions' which a man does not have and are a reason why it can be claimed that a man's love is relatively unconditional. (relative to women, of course) When conditions change, a woman's emotionally based evaluation also changes. Things may prompt a man to reevaluate a relationship with logic. If he leaves the relationship due to his reasoning, he might still be in love. Men suffer emotionally from parting longer than women. There is a study on that examining divorced couples.

Some people compare men and women seeking other sexual relationships as if they are the same whereas they are not. Women are are tendentially more hypergamous and men polygamous. That was a simple, but mostly accurate description. Without external influences, a man is likely to remain bonded and loyal to a woman even if he establishes a sexual relationship with another woman -- to whom he might also bond and remain loyal to. Genetic analysis shows there has been an average of 2 women per man who reproduced in the past of our species. I think that is an indicator polygamous tendency in men. If a woman surreptitiously has sex with another man, there is also the consideration of a woman conceiving a bastard and deceiving a man into believing the bastard is his child. The huge consequences for the man who would raise a child as his own when it is not. That is surely another reason for society consciously and unconsciously having a different attitude towards men and women who have sex outside of an established relationship which was presumed to be exclusive.