How does one go about getting their ex boyfriend back?

We have been dating for about 9 months now. We had a serious breakup about a week ago. He gave me a chance to fix everything. I know all my flaws, and I worked on it. Within a week he was extremely happy, so was I. Then we had a fight, and it was horrible. He doesn't want to see me or talk to me again. I don't know what to do now. I told him we were fine, he told me he knows this. I'm not calling him or trying to talk to him. I wrote in a card telling him how sorry I was, and that I hope sometime he will talk to me, or we can just be friends, and put it on his doorstep. This friendship/relationship is very important to me. I really don't want this to end it, at least the friendship we created. Is there anything else I should do besides leaving him alone? I'm scared that leaving him alone will make his feelings fade away. Is that possible?