GIRLS. What do u do about a boyfriend who denies the fact that he’s cheating??

So this is the THIRD time I find messages on my boyfriend’s phone to girls about fucking them and their “tight” pussy. Basically sexting. THREE TIMES THIS HAS HAPPENED. and let me tell u. I’m done, I’m leaving. But it’s so frustrating because he’s saying someone hacked his phone and sent those messages like how dumb do u think I am??? It’s frustrating because I want him to admit it but he’s so convinced that someone “hacked his phone” this is the most frustrating thing ever and I don’t know what to do at this point!!