I agree with what Ashlea & Kellie said.. my Mum read my diary too and it also shattered my trust with her. I felt so betrayed by her for such a long time.

IMO I don't think you should raise with him what you saw on his phone but as others have suggested I would get your DH to have a chat with him about "things".

Godd luck with it... I don't envy you. I am sure that in about 12 years time I will be wanting your advice as to how to deal with it!!