Are you asking how to learn to live with what he said ?, that he didn't want to marry you etc to another girl) or how to bring it up that you know what he said? without you having to admit that you snooped?
I don't think you will be able to get over what he said ( i wouldn't )
and i would tell my partner that i snooped , which is a lot less of a problem that the truth that you found out.
most couples are able to have full disclosure of their partners phones social media sites etc. Honest relationships with nothing to hide that is. In fact, i would shoot for that type of relationship.
My husband can read all my personal emails. If i've written to a friend talking about a bone of contention that we had, he wouldn't be angry, everybody needs to vent.
When did he say that he wouldn't marry you?
He won't let you break up with him unless you have a valid reason? I actually went to your profile to see if you live somewhere under Sharia law.
You can break up with him for any reason you like, and he doesn't have to approve.
Tell him you're done with his lies and you're leaving. Period end of story. He has zero rights to keep you in a relationship against your will. If he tires anything then call the police. Get a restraining order. Kick this lying liar out of your life and don't look back.
Whelp, he wants a valid reason--- so give him one. I agree that if I read that stuff, whether it was wrong to read or not, it would impact me forever more with that person. You now know the truth . . . that he is two faced and has a whole other side that thinks differently of you. I'd never trust him again and move on to someone that just loves you up front rather than having a side relationship (emotional or otherwise) where he spews what his other side thinks of you and your relationship which is negative.
Go ahead and tell him the truth. Tell him you were suspicious that he kept in touch with this girl, you got on facebook and read the messages between him and her. And you saw what he wrote and you are done. And if he is mad you read his messages--- you can say you were suspicious and you were RIGHT!! You had a right to be suspicious. Tell him you are not willing to be with someone no matter what he says to your face when he has said those things behind your back TO another woman. Not okay.
And you are breaking up with him. Who cares if he gets mad at you for snooping. Maybe it will give HIM a reason to okay the break up if he doesn't like snooping.
"He however says that he won't let me breakup with him unless I have a valid reason."
What are you talking about? Of course you can break up with him, or anyone at any time, and you don't even need to explain why. It's your life.
If you don't want to tell him that you read what he wrote, just say you don't think he is serious about marrying you, and you aren't feeling it in your heart that he loves you and is in it for the long haul. If he protests that of course he does, tell him you will believe it when he marries you. Then walk out.
I don't understand why you are acting so passive. He does not get to pronounce your reason valid or not, your heart is not feeling the love. That IS valid. It is how you feel, and that is as valid as anything he says.
I know exactly what you are going through because you describing exactly what happened to me only worse. I went to my wife's Facebook, something I never did because I had complete trust in her and she was talking to some guy saying the most horrible things about me, none that were true and having a real flirty conversation with the loser. In my case it only got worse and she ended up cheating! she had 2 kids before ad we have 1 together. I pretty much became the only Daddy the previous 2 only had and was happy to do so. My point is im stuck because 3 kids, but your not even married yet, thank God, you're gut told you something was'nt right and that made you snoop and you had the right too. Sounds like his is not a honest person ( like my wife) and just the fact he disrespected you like that is uncalled for. I would move on before its to late! If he was the right one for you he would of never done that in the first place.