So the ideal, perfect family doesn't exist at all?

We're 3 siblings; me the oldest and my 19 year-old twin sisters. Until recently, I thought we were one big, happy family. The ideal, perfect family but I guess when something is too good to be true then it is.

3 months ago, I stumbled into my dad's private journal and read it all. It took me a week to finish it and now I wish I had never read it. I'll cut it short:

- mom and dad started dating since they were 17 year-olds still in HS (they're now 50)

- mom she cheats in 1992 with his best friend in his own house. Dad catches them in the act, in the couch. He punches the friend (never speaks to him again) and breaks up.

- he gives in to mom's pleading, promises to never cheat again.. takes her back

- both work things in counseling, therapy, etc. They still get married in 1996

- I'm born in 1998 and dad still had doubts. He tested me twice and twice it came back 99.99 positive

- dad cheats back (mainly out of revenge) in 2000, had an affair for a couple weeks but guilt gets him and he confesses all. They worked it out again. Mom was more lenient with forgiving him and the R (reconciliation) process was faster since he confessed.

- They made a deal not to bring up each other's cheating anymore and never mention it to anyone, not even us. No cheating since and they still love each other, well in their own distorted ways I guess.

So much for the so called ''big, happy family'' teaching me morals and values to us. Ironically it was mom that was the stricter parent, lol. So the perfect family never exist?

Updates
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My initial shock is slowly subsiding by now. I guess their cheating history is none of my business and I'll let them continue keep their secret. They don't know I know by now but yeah it's going to be one awkward Thankgiving Day dinner this year, lol.
I never knew this. They never told me. They omit this history to me and everyone else in the family. My sisters and others in the family still has an intact image of them, just like I had before.
So the ideal, perfect family doesn't exist at all?
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