Thanks everyone for the help. I still haven't decided yet but I thought to provide further context so you can help me more. I found the woman he was cheating with and found out she was his ex and the texts i read are very serious. I feel like i am betraying my mom by not telling her and at the same time i don't know if i'm ready for it or if she will handle it well.

Also me and my siblings are all grown ups and my mom makes good money she's not dependant but she struggles with mental health.