My soon to be ex husband used to hate me going through his phone. I started out doing it out of boredom as well until I found things. Then I started doing it more often and always confronted him about it. He always get defensive and denied everything saying it was just out of boredom or in a friendly way. For example he would talk about getting with friends of his to sleep together and or something of that nature and he claims he was bored and drunk, or he would tell female friends of his that he had a history with or that he would be extremely flirty with in person that he loved them..
After so long he would just erase everything in his phone or facebook or whatever else he uses at least every 30 minutes. Proving to me that he is always hiding something. I mean I understand people deserve privacy and all, but at the same time that is a little excessive.