My neighbor is still married to his wife knowing she is pregnant for someone else. Why is he still with her?😬

I worked with a guy once who had a young child in spite of being sterile. If I remember correctly there was speculation the child belonged to his brother. Why? who knows. Maybe she had some redeeming qualities that weren't obvious. Maybe he wanted a child and this was the only way he was getting one. Maybe it was because there weren't many women willing to put up with the guy. Maybe it was cheaper to keep her than get a divorce.