The mechanism operates differently for men and women. In case of women, feelings instead of moods operate more dominantly in psychology. Most women cannot forget about the relationship for quite a long time when they break up with at partner and experience psychological pain since feelings are at work whether they still like the man or not any more. However, in case of men, only moods instead of feelings operate exclusively in psychology. When a man breaks up with a partner, he is likely to forget about the relationship instantly. The difference between men and women comes from the difference in the operation of moods and feelings in the unconscious.
When a woman begins to see another man right after she breaks up with her partner, it indicates that moods instead of feelings accompanied by psychological wounds are operating in this woman. Or it may be the case that the woman has so many wounds and she cannot stand without getting attention and consolation form men. After all, both seeing two people at the same time and seeing another person right after a break up are the manifestation of psychological disorders.
On the other hand, men seeing two women at the same time and seeing another woman right after a break up are the manifestation of moods being activated for fun and pleasure moment by moment. This is the underlying mechanism that applies to all men's unconscious. He just accidentally met a woman and got interested in her regardless of his current situation.