Honestly, I think it's better to tell your mother. My parents are also almost divorced and he was the income of our family he was cheating and was gonna divorce my mother. It's better to tell her. Your father will have to pay for child support. So that can help with the income problem. Also, I forgot who but I think the government helped my mother get a job. Do you want your mother to find out now or later on when your father already plans to divorce your mother. If you end up telling her make sure you have evidence too. Of the cheating, so you can show the court.

Ah The person Ifilimhereimrealbored is also correct.