Cheating Boyfriend

I need support, my boyfriend of two years has cheated on me three times in total with the same girl (plus an entire month of contact he swore they didnt have).. I am lost. I moved to a new city for him, I took him back countless times, and now here I am. Alone. While he is out doing drugs and partying with this girl who will never be true to him and help him get where he wants to go. I truly hate myself now. Why am I not good enough? Why am I too ugly , too fat, and too boring. My confidence is now non existent. Has anyone else been through simmilar situations? Can someone give advice?