Two years ago, my siblings told me they had caught my dad cheating on my mum with a younger woman he works with. I was the one who confronted him about it and he initially denied it, but after a few weeks he finally admitted it and promised he would stop. I told him we loved him and wouldn’t say anything to our mum because we didn’t want to choose sides and knew people make mistakes. A few months later, I received an email from the other woman and my brother confirmed that they are still sneaking around. Since then, we have been asking my dad to stop but he continues to lie and has started treating my mum badly. This is ruining the family and making it unbearable to be around my parents. Should I tell my mum – or should I get my dad to do it? I feel like I am betraying my mum and choosing my dad’s side. But I love my father and don’t want to hurt him either. •When leaving a message on this page, please be sensitive to the fact that you are responding to a real person in the grip of a real-life dilemma, who wrote to Private Lives asking for help and may well view your comments here. Please consider especially how your words or the tone of your message could be perceived by someone in this situation, and be aware that comments that appear to be disruptive or disrespectful to the individual concerned will be removed. •If you would like fellow readers to respond to a dilemma of yours, send us an outline of the situation of about 150 words. For advice from Pamela Stephenson Connolly on sexual matters, send us a brief description of your concerns. •All correspondence should reach us by Wednesday morning. Email private.lives@theguardian.com (please don’t send attachments). Submissions are subject to our terms and conditions: see gu.com/letters-terms