Toxic course mate(s)...

Hey guys. I have serious confidence issues with myself. Its not that I'm horrible at my studies or whatsoever. Its just that i feel scared in general. Maybe I'm over wary of things around me? Maybe i over-worry about stuff? I mean it could be good. But this gives space for others to trample all over me and this is bothering me a lot. I would really desire to boost my self esteem and gain confidence to do what I love to do without over thinking about that what ifs.

Im a collage student at the moment. And i am extremely passionate about my major. It was love at first sight and i decided to pursue it. Fast forward to my first year of college. I met this course mate, lets call her S here. Well, so we started chatting since there were rarely girls in my major. But taking classes with her became a nightmare. S seemed to love trampling all over me. She would demean me and mock at my intelligence. In lectures she go questioning me if I was really a college student for not understanding the lectures. She would mock the lecturer for spending more time to explain certain concepts. She would claim that she had learnt it all during the younger years and that these were all kids play. Being a freshman, with the little number of people i knew from my major, it dawned upon me that all of my course mates could be like this. Smart and wayyyy ahead of me. And arrogant. Day in and out i would be worried and overwork myself to make sure i was catching up well. I thought that I wasn't good enough to pursue my passion. I was learning what they had already know and I couldn't catch up at all. Gosh i was so stressed out. I hated school. I hated my major. Its so funny how one person could just ruin everything for you. And yes, I did try to avoid her as soon as I realized what she was doing to me. But she always managed to find me.

Well guess what. Plot twist. On the day of assignment submission! she approached me saying "Can you let me copy your solutions? I know how to solve this questions, but I'm not sure how to present them." What a typical excuse. There you are demoralizing me and trying to show that you're better (what for, honestly, we're all here to study and learn), and now you come to me telling me that you can do simple differentials.

Then i met my other course mates. Simply put, they were unsociable and prideful people, bent on competing with everyone else. maybe its the college environment. Maybe its how they were brought up. But honestly, I don't want to live 4 years in and environment where i see everyone as enemies. Doesn't help when my lecturers resembled them so much. I wanted to see everyone as fellow learners. Sorry for being cheesy but I'm a strong believer in the pursue of knowledge. This ate me up... I mean i went to college to learn and not to compete. I don't want to become like them.

Well, eventually, I got used to it all. swallowed my pride, and let them do their thing. Up my defenses but not fight. I want no trouble. But lo and behold, S comes back to me all the time. Am I that nice to bully? Cant she find someone else who is willing to play her stupid games? Somehow she is stuck to me like glue. Telling me she can't make friends. And goes leeching of my social circles. Well I'd just close an eye to it. A few more years and I'm gone from this hellhole.

In my second year, i decided that i would not do honors, as it would prolong my death sentence in this place. S heard about it and decided to follow suit. Declared that she would do so too. I didn't much of it honestly. The next semester, I felt inspired my a certain lecturer, and decided to work in his lab for honors year in the future. And guess what, she decided the same. (what are the odds, the department has lots of profs to choose from) The next semester, I decided to pursue a specialization in my field, and yep, she decided to follow suit. Under the recruitment of a prof which i hit off quite well with, I decided for honors year in his lab instead. And yep, same story. And now i decided to pursue postgrad studies, and she decided to follow suit. I mean yea its her life and her choices. But why is she so bent on following me and trying to make my life hell? I made my own decisions and put in all these effort to pave the path i would like to take. And there she goes killing of my confidence and stealing my efforts, riding on my coattails. what did i even do to her? nothing!

Sigh... sorry for the long rant. I would really like to leave the grasps of this person. and walk my own path, without her chasing after me and psychologically torturing me.
And advice on how? I would not like to create trouble and I really want my confidence back.
Thanks for reading this! I really appreciate it!