Why am I always disappointing and hurting him?

Here I go again, back on the wicked roller coaster ride in which I destroy everything in my path. I make these promises and then I break them. I hurt him over and over and over and over again. He is so tired of hearing the same old shit from me. I'm sorry, I didn't know what I was thinking. Why do I continue to act this way and hurt him and annoy him to the point where he doesn't want to be near me. He resents me, the love we once shared has been shattered. Why do I feel like I've just ruined everything, our world crashing down. Yesterday was so wonderful and just like that I mess it all up. Everytime I say I am trying, I do try, and then I blow it up. And then I say I am trying, and I do try and I blow it up. I must not be trying hard enough, but I think I am, but I guess I am not. How can he stand me? I can't even stand myself right now. We talked yesterday so openly about these issues and I tell him I am going to prove to you that I am not selfish and I can be open with you, and then today I just flushed it all down the toilet. How can I possibly go to him and look him in the eyes and ask him to forgive me? I can't even forgive myself. It was just yesterday we went through all this and here I am today living the nightmare all over again. Why? Why? I have not answers, just questions. I can't imagine how he feels, because I feel so sick to my stomach, so he must feel it too! How can I do this to someone who cares for me so much.