What is wrong with me

I love him so much. Sometimes I think a little too much, lol. I wanted to spend my whole life with him. We have been together for 5 years, but for the last year and a half he's done nothing, but cheat on me constantly. He swears he loves me, and hes just stressed. "I'm so sorry, you deserve better than me. I promise I will change" is what he tells me. I realise how much I love him, naively have a sliver of hope he will return back to the man he was when I met him, that he will truly change. And I stay. I try to go over everything in my head that's possibly wrong with me for him want those other females. I lose myself a little more each time. The most recent one was on Thursday. The day after new years. The day after I stood there and told him how much I love him, how much I want him, and how I am so blessed to spend another year with the best man in the world. What the fuck is wrong with me?