I'm going to leave my friend behind after we made plans
Why are you leaving him behind?
I hated him right from the beginning, but now I can't even stand myself around him anymore
You don't have to like everybody. But you're no friend if you hate him, and you should be reliable and keep promises made.
I can't help that I have to hang out with people I don't like.
You don't have to hang out with anyone you don't want to. You should just invite him out this one last time then never again.