Men give one very common reason that their partner is disgusting. Mainly people who are in long-term relationships, they get frustrated with the same person. They give excuses that she has gained huge weight, and she has a drinking problem and many more.
The very common reason which men give that their partner is a changed person now. These are the very common reason why do men cheat. This kind of problems does not occur in a single time. Sometimes men get attracted with to gorgeous women who may be walking around them. Sometimes women attract men for sexual intercourse.
Men basically cannot say no to a woman when they offer for sex. Men generally have a weakness for an attractive woman. They cannot stop themselves from dating an attractive woman.
When a woman ask a man that he is single or not, then men generally say that they are single being in some other relationship. Men like to feel attractive and wanted by women, and when they get this kind of expression from a woman, they tend to fall in that direction. Sometime men get involved in harmless flirting and later they get attracted to the woman.