I feel so lost

How can he move on so fast? Less than a month ago he wanted to marry me and now he begs me to leave him alone because I stress out his mind. He tells me if I try to speak to his family about what happened then he will never come back, but I aready know he will never come back. He says he's happy, his life is good and that he's finally finding himself but at the same time he tells me he's in pain, that he hates me, that I stress him out, that he dropped out of university because of me, that he left the country for a few weeks because of me. I didn't even do anything but tell him that I'm tired of being treated like a crap and him justifying it by claiming he's simply depressed.

I hate myself for still yearning for him. Every hour, every minute, every second his name, memories of him, our conversations just reply in my mind. I keep debating with myself all day on whether or not he'll ever come back. How do you forget someone so fast? In less than a week he was gone and it's been a month now he won't change his decision. This hurts too much, I just want this pain to stop. What has happened to me? When did I lose myself like this?