There is nothing wrong with you at all.
You deserve much better treatment than this.
I'm no expert, but IME it would seem that he has checked out of your relationship and is looking elsewhere.
There is a well worn script to this, they deny and delete. Deny any thing has happened and then delete all of the evidence.
Oh, there's another D too, deflect, try and deflect the attention elsewhere ie saying you shouldn't have looked at his phone....
Nothing wrong with that at all is there...? He shouldn't have had the stuff there in the first place.
These pics on his email account. Where are they from? I mean, is it a dating site or something ...?
The text message you found when he'd been out sounds like it could of been as a result of a first time meet arranged thru a dodgy dating site.
You need to either print off or get screen shots of the text messages and emails. Or forward the emails to yourself. Remember to delete from the sent mail. It's also worth checking the sent and deleted mailboxes too. They can be a wealth of information, sadly.....
You need to be discreet and you need to realise that he will lie his way out of it if he can. He will also try and turn it round onto you, maybe even making out its your fault!
I'm so sorry you're going thru this.