"she started saying that she has NO REASON to cheat on my dad"

As the above poster, it's not your business, it's VERY intrusive to hack someones phone to get to their personal information and you've no right anyway.

This is between your parents. Having 'no reason' to cheat on your father doesn't even come into it. If she's not emotionally satisfied in her marriage and has gone outside the relationship for fulfillment, it's nothing to do with your dad being a great guy.

People break up all the time, people live within unfulfilling marriages and all sorts happens.