I'm going to cut off my friend because he started dating a girl I had feelings for and am trying to get over.
Why did you have feelings for her?
I saw her as my love and I'm angry he managed to do this to me
You shouldn't end your friendship over a girl. Your attraction to her might be fleeting and you might not be able to repair your friendship.
No, I'm going to hate both of them forever.
I understand that you feel that way right now, but once some time passes I'm sure you'll feel differently. I don't think you should ruin your friendship because of you feel currently, because I think you'll regret it.