I'm going to cut ties with my best friend after they ditched me for somebody who used to bully me
Why do you think they left you for the bully?
I do not know, but I am angry at him.
If your friend left you for someone who was a bully then they are not your friend. You should definitely cut ties and move on.
I want to get revenge on that douche.
I know you are upset at him, but getting revenge is not the way. You would be no better than the bully if you were to do that. Just get them out of your life and leave it at that.