How can I trust him again?

My boyfriend and I have been dating for about 8 months now. He’s cheated on me several times, not physically but he’ll message other girls telling them things like “you’re beautiful” “you’re goals” “you’re so bad” or sending heart eyes. I have tried to forgive him in hopes that he’ll change and I believe him when he says he’ll stop, so things have been great lately. We have stopped fighting, but I felt like it was too good to be true. We also deactivated our social media account and deleted the apps from our phones almost a month ago because they were also causing problems in our relationship. Two nights ago I slept over his house and decided to look through his phone, everything seemed fine. Then I decided to download Snapchat and obviously I don’t have the password to that so I reset it and the new password sent to his phone so I immediately deleted it and finally was able to log in. Turns out he’s been cheating on me this whole time. I found Snapchat messages everyday from him talking to other girls. Telling them he wants to fuck them and telling them that I’m “dick whipped” and telling them they’re beautiful and things like that. I found all this out at 3:30 am and woke him up and he has apologized and tries to justify himself by saying he has been cheated on before so he can’t trust anybody so he does it not to get hurt. I’m the past 8 months I have been nothing but loyal to him and he say he does it because he thinks I’m cheating even when I have proved to him I don’t cheat. For the past two days I have been balling my eyes out and he still barely talks about the subject. When he sees I’m crying he asks me to stop and wipes away my tears and all he says is “I love you” but I don’t believe it and now I reread all those messages and I’m in complete shock. What do I do??? Any advice ??