It's an all around shitty situation for everyone tbh. She was forced to marry and have a child. I understand why she ran away. The state of women's rights in Japan are abysmal then is still abysmal now. However, O-ten is probably would have a better life in Yaetatsu's care, he would not make her marry and is probably content with just seeing her happy.
LET HIM GOOOO AHHHH