I think it really depends on the relationship between your Sim and her husband. I did a similar thing with my Sim, when her husband became an elder she cheated with a younger guy and had a baby. When it came to the crunch, she broke up with the jealous lover, and repaired the relationship with her husband. He brought up the child in the same way as his own earlier kids, although it was clear in the family tree who was fathered by whom. My female Sim had a very high charisma, though, so that might have helped.