People stay in marriage because they need it. Once they don't need it anymore, they seperate.
If they have to split the house, money, custody, and there's too much pain to get divorce, then couple stay together.
If they feel easy to get divorce, or the cost of divorce is very low or even negative, they divorce.
So think it this way, the cost of marriage vs. the cost of divorce decides whether a couple wants to stay in the marriage.
The cost of marriage is equalvalent to how much they can tolerate each other or if there's too much pain or potential loss in this relationship . Love is really a very small denominator in this equation.
