ANSWER: You should do sujood as sahu since you sat down and did tashahhud before realising your mistake.  Sujood As Sahu (Prostrations of Forgetfulness)

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ANSWER: He is sinful for treating her like that especially when she is older than him and taking care of his child.  You should keep them away from one another so that they don’t meet and he doesn’t get a chance to mistreat her like this. 

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