HE'S MAKING ME CRAZY!!! 😠😕😢

I've been with my S.O for about 1 year and a half. At 1st things were GREAT! Now he's slowly turning into a complete DUSH BAG! About 6months ago I caught him on FB talking to girls Via inbox. I confronted him about it and we've moved on. 2 weeks ago I find a video of a random girl in his computer and she's showing him her "Dress"(Boobs). Of course he DENIES it and says he doesn't know her. NOW today, on Facebook, he's liking videos of girls and shit. I'm THIS CLOSE to just saying FUCK THIS RELATIONSHIP! I'm so worn out, and tired. 😟 What would YOU ladies do? I just feel so STUPID!! 😩