I feel weak right now, what do you think?

For next semester, I have an elective with the girl who litterally made me hate life. She is one on those lucky people where everything works out and so it sucks watching her love life when she made me hate it. Anyway, in this class, she is with all of the new friends she has made (first year of high school) and even though I dont know any of them, they allready have opions formed about me because she has talked about me to them. I know if i see her having fun I will get jealous and discouraged. I am a quieter person to begin with, so no matter how much I tell myself to be more outgoing I just cant. I dont want to spend my months building more emotional stress because I get more discouraged and feel more lonely but Im also hesitant to change electives because its the what ifs I hate like I make friends or change these girls opions. At the same time, I know Im not exactly "emotinally stable" right now. What do you think I should do?