How can I win this guy back?

This guy is one of my best friends. He used to be infatuated with me, but I was interested in another guy then so told him to move on. Since then I've done a lot to break his trust in me. After spending more time with him, I realize that I am interested in him. Today I asked him how long it took him to get over me(initially he said it wouldn't take long at all) and he said that he never fully got over me, he just stopped caring. He also told me that he was kinda interested in another girl. How can I win him back, and regain his trust?