My mom actually cheated on my dad way back when I was entering my first year of high school. My dad knew I was a giga tech nerd at the time, so he told me he had some suspicions and asked me to find out who she was messaging by gaining access to her phone somehow.
My mom had changed her phone's passcode at the time, which was a huge red flag.
She was always very secretive when using her phone and made sure that no one was looking. It was pretty obvious, even my prepubescent dumb ass knew something was up.
I decided to help. I sent her a phishing email that looked just like icloud but it said "Someone had tried to sign in, please change your password" or some bullshit like that which lead her to a temporary phishing site which was literally just a copy of icloud's sign in page at the time, but it had an extra form field for "new password" and "old password". Her dumb ass actually fell for it even though I didn't actually buy a proper domain and it was just a subdomain from some shitty free hosting service that looked like garbage.somethingapp.com she actually entered her password which was logged to me with a simple HTTP request.
After that, I gained access to her icloud account. Because she used imessage for sending messages, all I had to do was sign into imessage on my mac using her icloud account.
But man was it brutal. When I signed into her imessages on my mac for the very first time, I could see her whole stream of messages and people that were messaging her in real time. It was brutal having to witness your own mom cheating on your dad firsthand. It really fucked me up as a child.