There are, of course, people who prey on others for material gain, both men and women, particularly where the elderly and vulnerable are concerned. And maybe some people marry for money or position or to gain a passport. Who knows?
However, romantic that I am, I do believe that most people marry for love, but often it just doesn't work out, and then the separation can become bitter as the parties scrap over children and possessions.
Nobody knows what goes on in someone else's marriage, even those who are close to you, so it doesn't do to speculate.
Diana, if what you say is true, and if this whole thread is not a 'wind up', you made your marriage work. It may not be the sort of marriage I would want or, I suspect, one that many posters on here would want, but you say that it is what you wanted.
So why are you so bitter? Did you never really forgive your husband for the affair? Did he destroy your self-esteem, to the extent where you felt you had to 'win' him back instead of the other way round? Did you ever have a career of your own, which would have given you more confidence and independence? Do you secretly regret some of your life choices?
Obviously, none of us can know, but I do hope that your daughters have higher self esteem and contentment than you appear to have found. I find it surprising that a mother of three daughters would have so little regard for the female sex. You should be their role model and inspiration, as well as the person they love and can turn to for support. Do you actually have much of a relationship with them at all, beyond the superficial?