Cheating

So my partner came over tonight and I grabbed his phone to go through his music (with his permission)

He and I met online POF. Anyway I saw the app was still on his phone. He was sitting right next to me I wasn't being sneaky at all so I clicked on it and he says "oh i still haven't deleted that app" THEN i went to click on the messages logo and he literally hit the phone out of my hand. So I just looked at him like wtf?? Then he says he just doesn't want me seeing any messages he sent to other women when we first started talking. Then he got all nuts and said he doesn't like people going through his phone and that he never tries to go through mine so I shouldn't go through his. Then I said he was right next to me and it's not like I sneakily stole his phone or anything and then I told him his reaction was super over the top and made me very suspicious of him. Then he tried to give me some long haul story about how his ex would constantly go through his phone all time etc etc. It all seemed very . . . Rehearsed. Like why have such a reaction if theres nothing to hide? So messed up. Do you think this is simply a case of he wants his privacy or he has been messaging other women and just doesn't want me to see? Either way the trust is completely gone and I'm going to dump him. I just want to know if you ladies feel like I'm justified in dumping him over this?