I am sorry you are going through a tough time. Maybe not tough now, the last time you posted was in May.
So far as men sticking with women and women sticking with men, there is a book written about that called "His Needs, Her Needs". Men's needs are very different from women's. Of course this is generalized but I found it true on a lot of levels. The number one need of most women is security. A stable man, strong, hard working, ethical, a provider for the family. Most women will give up romance and other needs to keep their security. This is why women will stick by a man. The number one need for most men, believe it or not, is sex. The second most common need is respect. I believe that if a woman allows sex with her husband he feels respected; it is a two prong need. If a man is no longer getting sex, his number one need, he often turns to other ways to find release. Whether that is a mistress or porn or whatever. This is a generalization but often times a stable and successful man whose wife is sick finds a woman at work who shows him respect, casts her snare on him, and he falls in love with her. He is not getting sex at home and his brain tells him to go where the sex is.