Also, I hate how people are just like "The protagonist isn't standing up for herself, she's weak and easily guilible" even after reading her GOD DAMN BACKSTORY!
"She doesn't talk about her problems-" yeah, go talk about your problems to some school councelor that seems to not even want to listen to you or a random adult (professor or not) that'll just turn a blind eye on your situation because it can be a hassle to take care of. And don't get me started on her family.
Why do you think that I compared this to LIFE? It has the same logic behind the silence of their main character, because it's logic. And I've been bullied, I know that feeling that even if you talk about it, sometimes it'll get worse.
Also, when you suddenly lost EVERYONE around you because of some shaddy rumors, after your relationship was so good, and the feeling that it was just a repeat of so many experiences, won't you yearn for the love of someone? People get desperate in hard times, they'll even sometimes lower their guard when they need help. It's not unnatural for Mc to start having fun with this girl even if it's not good.