I saw something that shouldn't been seen by my father

I was snooping through my dad's messages app as most of my school messages comes to him. So while i was snooping, i accidentally checked the conversations between him and my mom. Both of them were separated since 3 years ago and my father is remarried and my mother has a boyfriend. So i was checking the messages, suddenly i saw a long message and i recognized fastly as i was the one who wrote it in my OWN phone. In that message i was explaining about my mental health problems and many depressing things and it was like an essay that i sent to my mom. The question is how did he get it and why did he send it to my mom again, she even replied ok to him. And in my phone i never sent that message to him and he never talked about it also. It was very personal as i tend to send essay like messages to my mom as she knows im mentally weak eventhough im not diagnosed.