The day Satoru was forced to marry Yumi was the worst day of your life you had been deeply in love with Satoru since high school but you supported him even if it hurt you, the day Shiro was born you swore to protect the boy no matter what but a month after Shiro's birth Yumi divorced Satoru and gave up custody of Shiro leaving Satoru alone. To make sure Shiro has a mother the Gojo clan made Saotru marry you which was the best thing they have done in a long time.