He told his ex he is single BUT we've been together 3 months... PLEASE HELP!

Hey ladies, so I have been seeing this guy for about 3 months now. We went to highschool together and have alot of history (good and bad) we have always dated on and off, but the last time we broke up we stayed apart for about a year with no communication. Anyways, we have been back together again and he has been staying at my place. We have talked about the past and our rough patches and he promised me he is serious about our relationship this time (he has cheated in the past). Well tonight he passed out early and his phone kept blowing up, so I reached over to mute it and when I did I saw all these messages from his ex. I know his password so I unlocked his phone (this is so not like me) in the text from his ex she asked him if he was seeing anyone and he told her "nope, no one". I was crushed and instantly felt betrayed. BUT now I dont know what to do about it, I feel like I cant confront him because I had no buisness being in his phone... but at the same time, he has no buisness telling his ex he is single when he obviously is not. WHAT SHOULD I DO?! I need your help ladies!