How am I supposed to move on from this?

I recently broke up with my boyfriend of 3 years, and it was completely out of the blue. He came to my house for dinner and broke up with me through a one page note. Yes, through a NOTE. Even after three years, he could not even have the decency to actually try to work things out with me. While I have been doing well dealing with it, I feel as if I do not know how to move on from it. He knew everything about me, and the way he broke up with me basically threw all my emotions and problems I had shared with him in the 3 years back in my face. Does anyone have any advice that would help me officially move on from this, and be able to trust another guy with my feelings again? I really dislike dwelling in what he did to me, but it has honestly damaged me to the point where I believe that I just deserved what he did to me. How can I get myself back into a positive mindset where I can allow someone into my life as I did him?