My mom cheated on my (now deceased) dad, and i'm the only person who knows?

To give some info, my father died of cancer when i was eleven, and he was in and out of the hospital for most of my life. (i'm a sixteen y/o girl, youngest of five) my parents always had a loving relationship (married 25 years) and stuck together even through hard times. I was hanging out with my mom and i used her phone to google something because she asked me to, and when i opened her phone it was at her texts & she had written a a long passage to her 'boyfriend' (this is in quotes because they used to date, got into a fight and date on and off now). Her phone froze on the screen because it's an older iphone and it's slow and i read the message. Apparently they've been in a relationship for ten years, even though she introduced us to him a year ago under the guise of meeting a few months before at work. If you do the math, they were in a relationship for five years before my dad died. In addition, she has been coming home way later than usual under the guise of having extra work but she has actually been seeing him secretly (also in the message). I know i shouldn't have read what was on the screen so i'm at fault, but what do i even do? I understand that my dad was sick and couldn't exactly be the 'model husband' all the time but to cheat is just unthinkable. Should i confront her? Should i tell my siblings? What do i do i'm so confused and upset.

You're a terrible person blocking

The right thing is to keep quiet and say nothing. If you talk to anyone about it, you cause all sorts of upset and trouble. Just do the right thing and keep quiet. Talking about it will not benefit anyone. Do not be a blabbermouth.

What she did is definitely wrong, but it is water under the bridge. She didn't hurt you. She hurt your dad. Your dad is gone. This was his to complain about, and he isn't making a complaint. Don't worry yourself with it. If you think this could become an issue between you and your mom, maybe you should ask her about it and have a heart to heart to get your feelings out there, but nothing is going to change the past, and you probably won't change your mom's behavior either.

You can't fix the past. Let go of it. Let it be a lesson to you to make sure you do better yourself. That will make it into a worth while learning experience for you. Don't let it eat on you. There are no perfect people.

How do you know your father didn't tell her to meet someone new so she woldn't be alone after he died? You don't. Keep it to yourself.

What good would it do to tell something like this. It certainly won't bring your father back. Try to respect your mother's privacy. She's been through a lot and so have you.

Drop it…

She has needs. She is person. She used to be a girl who went out and had fun, until you were born.

People are not meant to be monogamous

I would just stay out of it since there's nothing you can do about it anyways