He's not sorry for what he did, he's sorry that he was caught. This has been all about him he feels like crap, he wants you to love him again, he wants to go back to the way things were. What about you?
On Thursday night this man was reading your messages upstairs as you were writing them. And then he came back downstairs and asked you if you'd contacted ex. Clearly designed to catch you out, doing what exactly? Given he's going away for a month the iPad would presumably have been going with him, y'know, so he could read your messages on it while he was away. what else is on the iPad? facebook? mn? other means by which you can speak to people?
If you hadn't caught him he would have continued reading your messages, for how long I wonder? He has been reading your messages for weeks. He knows there is nothing going on between you and your ex, or anyone else, and yet he is still reading them. When I realised my ex was doing this he said "I know that there's nothing going on, I was going to stop anyway." to which I responded "but you didn't, did you? You knew there was nothing going on and yet you continued to read, and to make remarks based on things I'd written." He couldn't answer me. And he had my fb/twitter/other accounts set up on his phone so he was getting notifications of any messages I received.
Even if you were to go through therapy and he swore never to do it again you would never be able to trust him again. You couldn't get to a point where your phone was an open book, where you felt you could give him a password or access to any of your devices, and you would always wonder whether or not he knew who you were messaging, every time he made a comment which might have been near to something you'd written to someone. And then there would come a point where he starts insisting that he can be trusted again. Except your phone and your messages are private, so you wouldn't be obliged to let him in, and he would make it all about him again.
That feeling of being watched is one which doesn't go away. I am years on from it and still sometimes I get a feeling that ex is still watching what I'm doing by things that my dc come out with in terms of what he's said to them.
This is not just reading someone's text messages. It is gaslighting, abusive behaviour, designed to make the op accountable for everything she does, says, etc.
Eventually I stopped going out. stopped seeing friends because it caused issues between us, and then he started saying I should get some help because I'd lost my confidence.
I am 
that people feel sorry for this arsehole. If he was beating the op up because of his past would we feel sorry for him ? no. Insecurity takes many forms, and while if he has been a genuine victim of violence he deserves sympathy for what he went through in the past, the way he has chosen to react to it is his responsibility. But I wonder what the ex would have to say for herself, and whether there is in fact more to this.
This man is emotionally abusive. He has gaslighted the op for weeks, and would have continued to do so but for the fact she found out.
I have been on mn for over ten years and I am rarely of the LTB persuasion. And yes, it could be said that I am projecting from my own experiences, but it's ones experiences which do give a perspective on what it's like to live in that kind of situation. You can't actually know what it feels like until you've experienced it. I had nothing to hide and my xh had full access to my phone, email, etc. All he had to do was have a conversation if he felt insecure. But instead he had to go behind my back. I still have nothing to hide, and my dp can pick up my phone, computer etc whenever he wants. It's not the need to hide things that is the issue, it's the need of other people, the op's dp in this case, to see things that causes the issue.
Op, you have a month without him now. this is IMO a good thing. This gives you time to re-discover your independence, become your own person, learn to live on your own again. And when he gets back throw his gaslighting abusive arse out the door.