I found out my father was cheating on my mother. I already knew about this 4 years ago, I tried confronting my father and the girl he's talking with (online) about this (they were batchmate or blockmates back in college or high school, I forgot). My father told my mother and my father gave a believable explanation, he gaslighted us so much and laugh it off. Until I found the same thing this year. My father has been away since I was a kid and I've been my mother's support ever since, given I am his eldest daughter. The thing right now is, I can't tell her or my sister about this. I don't wanna ruin our family and we still needed our father because I'm still on my third year in college and my sister's in high school. Everything's weighing down on me.