How to act around a bully?

Let’s call him Regina George because they look alike. I was in the same class with him and this guy was being condescending in the last semester.
Also, he knew about my life because a friend of him was his flying monkey that was giving him information and she was my classmate as well. Plus, I helped her with class ( I felt bad for her since she was falling). When I notice she was talking behind my back, I made up a bunch of tragic stories like a telenovela actress bc it was funny how she actually believed it and told him.

Going back to Regina George, he used to stalk and pass by me extremely fast so I could notice him. He used to clear his throat during the entire class and when I looked at him, he sat at the back of the class to continue with that. After class when I was going to talk to the professor, he stayed in class staring at me like a maniac and when I said to my classmates I was going to reunite with the professor, he went to his office. When I saw all of this cringe, I didn’t want to reason with that thing so I remained silent. I didn’t care about him because he was nothing important (he doesn’t have a job or internship, not a leader, no car or ambitions and he’s not into any association in college).

Now, our dear Regina George walks like a diva and acts like he did something that contribute to our society.

I feel weak for letting him win and dumb for being nice to his flying monkey. The only thing they did was to gain confidence at my expense.