Relationship help

So I just found out that my boyfriend of three years is cheating on me again. I was on Snapchat and found his and when I asked him about it he got mad and told me he didn’t have a Snapchat. Last night he was sleeping and his phone kept going off so I looked and it was snapchats from different girls. I unlocked it and looked at them and it was all these girls sending him sexy selfies and shit texting him telling him to call them. Then I found out he is also on a dating app. I’m so broken. I haven’t told him I know yet. It hurts soo bad idk what to do