How do you stop the sadness?...

I can't let go of him.  He's in everything I see, and everything I do.  He's still a big part of my world, and I'm probably nothing to him other than his first love.  I wish it ended differently.  That he didn't give up on me and on us.  I miss him every single day.  Sometimes it hurts so much that it gets hard to think or function, and I break.  It's so overwhelming, and it takes up all my thought.  It's been over a month now, and I still cry every day over him.  I feel like I lost such a huge part of who I am when he walked away.  I just... I miss him.  I feel like I need him, but he doesn't need me.  I know I need to move on, but I just can't do it...