Not good enough?

I met my now ex bf when he was going through depression and I became his support. Outside of that everything was good or so I thought until he started to mistreat me and become emotionally abusive. He pushed me away and basically tossed me aside like I was nothing or no one to him. I never gave him a reason to mistreat me as far as I know and my heart is broken into pieces because he so easily switched up on me. I can't help but wonder why he did that and if I wasn't good enough to continue being his gf? I also can't help but wonder if I were his ex gf before me if he would have treated her this way because I know that he wasn't fully over her. I don't want to question or doubt my self worth but I can't help but wish I was good enough. How do I stop This? 😔💔💔