Rumour has it that three quarters of heterosexual couples that break up do this on the woman’s initiative. The usual explanation is that women tend to expect more from relationships, so they’re disappointed sooner. Another explanation I’ve heard is that women tend to take more initiatives than men when it comes to relationships.
At least in the West, this needs some correction. In the case where children are involved, women in the West can more or less count on staying in care of the children. Men cannot take this for granted, hardly ever.
This means that when children are involved, the choice to leave your partner is a totally different one for the man than for the woman. The woman only has to decide whether to leave her husband. The man needs to decide whether he wants to leave his wife and his kids. Surely this would account for a greater reluctance in men.