Their instincts are to mate with the best available male, attain security for their offspring, and raise their children. Long-term love or nuturing of a man is not part of their programming, except to protect their brood. If they believe they can raise the children alone, they will often do so, its easier for them. Female nature is to bear children, not compromise with men. Women do not need (or want) men around, for the long term. Understand that the beginning of a relationship with a women is really the beginning of the end.