Once a Cheater always a Cheater?

If you are in a relationship where your partner cheats is he liable to cheat again? I have a friend who stayed with her husband after she found out that he had not only cheated on her but also fathered a child with the other woman. She forgave him but she never quite trusted him again. She stayed with him for the sake of their children, and she made it a point to accept and welcome his child with the other woman into her home and family. Was she right to do so? How did that affect her children? do you think that her husband appreciated the sacrifice she made, or did he feel its what she should have done if she wanted to keep him? I always felt that she sold herself short because she deserved so much more. However, it was her decision to make and I supported her decision. My question to you is this, would you stay if your husband or wife had a child from their affair? Do you think that he would cheat again and expect forgiveness again? How much of yourself would you sacrifice to keep a relationship?