at first i wanted to be harsh to dude but like someone else said, people grow up differently...
-first of all, you most likely only know what your mom told you. And the reason your dad doesn't open up to you about his side is probably because he knows you're not mature enough to handle things...
-second, this is gonna sound tough but your dad doesn't really owe your mom or your sisters shyt at this point. from your own words, SHE left him. He tried to get back with her. She wouldn't take him back.

He told her she'd fail if she doesn't take him back and now you're saying she's struggling...i'm saying...
-third your parents are seperated and SHE left him and wouldn't take him back. I would
HOPE dude is getting some other p*ssy...sheeeeeeit...
-fourth, you went through your dad's phone without his permission and the first thing you did when you found out what it was is tell your sisters?

your sisters probably already told your mother too...

then you wonder why your dad doesn't open up to you about stuff like that???
here at the coli we're like a family so i gotta keep it real with you. you need to grow up a little...