What am i supposed to do? Where do I go from here?

I was in a 16 month relationship and it recently ended. A week later he was dating another girl. He didn't want to date but she talked him into it and he kinda liked her so he just agreed to go out. He still wants to be friends with me but its hard for me. I'm still in love with him, and he says he still loves me but he promised her that he wouldn't leave her for me when they first got together. Well now its been about a month, I'm not better off and he said he's starting to get feelings for her.. but he also told me that he's seen the changes I've made and that if he wasn't with her already he would actually consider tryin to work with me again. I'm tryin to get over him but all the things online say you have to realize that the other person just doesn't want to be with you. and in this case that's not true. Part of him wants to be with me and the other part likes the new life and new girl he's with. I need to get over him. I can't stay in this limbo. I want to be with him so bad, but i can't and I need to get over it cause I shouldn't be his like, "back up plan": or whatever. I need to get over these feelings i have for him. how do i do this? what steps can i take?