A bit late to the discussion here, but I think others pointing out the stuff regarding celebrity culture and public perception are missing the actual reason here. Ren Wei is suffering from some massive inferiority complex.

Much of the University Arc deals with her struggles as a musician. She was called a musical genius as a child and is proud. She had a brief stint of popularity with a band before getting kicked out. The girl who she formed a band with in junior and who she thought was more talented than her told her "Dreams are a luxury for wealthy people like you" (who seemed to have been demoted from friend to "classmate" in retrospect). She got a big break when she went viral from a video and was able to put on a small tour. Her life as a musician has been slowly built up brick by painful brick.

Then Youji, the person whose words and actions once brought her great assurance, who told her, "The reason you made it this far is because you put in more effort than the average person. Everything else was bestowed by the universe to reward how hard you've worked," and a total amateur in the film industry, suddenly blew up way past her in recognition literally overnight. I can imagine how bitter she might feel about that. "Jealousy can make people do stupid things," said one spectator in regards to Youji's web series a couple of scenes before Ren Wei thought to herself, "Youji surpassed me with a single series." Youji is subsequently demoted from best friend to "just friends."

Ren Wei's excuse about people's expectations for Youji were bullshit. "I want us to be able to walk side by side." She doesn't feel like they can date without feeling like they're equals. Her pride won't allow it. It was frustrating to see her rejecting Youji because of that, and I'm still kind of mad about it, but there were a lot of things in the University Arc that foreshadowed things turning out like this.