Learning How to Let Go

Quite a lot of time has passed since my break up...but it feels like nothing compared to how long we were together. Since we broke up, he has been nothing but hurtful to me. His words have been mean, his actions have caused me pain. He started seeing someone else only a month after we broke up, and now calls her his girlfriend. I feel so replaceable, so easy to forget, so insignificant.
And even though I have felt absolute heartache, because of his actions and words, I just can't shake him. I still love him. I still want things to work out. I hate myself for that. It seems so weak and pathetic.
But I think it's because I chose him...I don't let people into my life too easily, and I let him in. I made him part of my family. I chose to love him every day, even on the tough days, even through the hard times. And now I am supposed to just move on, forget about him, convince myself I can do better...I don't know how to do that. It's like asking me to forget about my sister, or my mom....I don't know how to stop loving him. I don't know how to cut that off. And maybe that is my own problem..maybe that is a weakness of mine.
But no matter the reason, my inability to let go is causing me so much pain. I just want to feel better. He took a part of me and I want it back. I want to feel whole again.