Most Helpful Guy
I'd say you should talk to him and apologize. Explain that you love him and were feeling insecure and that you made a mistake. And that you trust him and won't do it again. If he doesn't want to talk about it, or rejects your apology, then it probably means there is more to his wanting to break up than just this. And it may not be reconcilable. You may have to accept that it's over. If that is the case, lick your wounds and learn something from the experience. As long as you learned what went wrong, the relationship was not in vain. It's very difficult, but something everyone has to go through in life at one time or another. You will survive and be better off in the end even if it cannot be repaired.
Most Helpful Girl
if you've gone through his phone that means you don't trust him, now he knows you've gone through his phone he's not gonna trust you.
If you do get back together your relationship won't be the same. He'll be reluctant to leave his phone around you and you'll be too scared to say anything in case he dumps you.
If you're prepared for that then just talk to him. Tell him that you love him & that you value him. If he wants to get back together then speak about the issues you have with him the 'few other changes' you mentioned. Tell him you don't feel 100% secure or comfortable, ask him if he can give you an explanation for the texts & then start fresh. If he doesn't want to get back together then leave it. You can't force him and maybe it's for the best, maybe you're the one who dodged a bullet he could've actually been cheating after all.