“I’m dealing with family grief and cheating”

A couple months ago, my grandmother and aunt died in a car accident. My mother was devastated, seeing as losing your mom and sister is really rough. Although I have mostly accepted it and moved on, my mom hasn’t really. She is definitely an emotional person and I don’t expect her grief to last forever, but it worries me how much she cries when she thinks no one is looking or is in a depressed mood.

My dad has not been much of a source for support to her either. He was kind to her at first but now he mostly keeps to himself. They have been married for 20 years but recently, my mom found out that he was cyber cheating on her for sixteen months. I have no idea what to do in this situation, the tension in our home is so high and I hate to see the situation breaking my mother like this. Please help.