That sunbae is future jail house material. I'm glad Yuta is looking out for her but I also don't think we've got the full story from him either. I could be over thinking things, but I feel like there is more to his background or his interest in her. Not necessarily bad, but just unknown.
I've also said it in previous chapters but like
@Miyono-chan I really wish she would sit down and make her friend listen to what her boyfriend's been doing. She can show his texts as evidence too. Even if her friend doesn't believe her, at least it's her choice at that point rather than being in the dark. Also if he's getting forceful and stalking her, he's beyond just being a lousy cheat, he's dangerous. As much as her friend is in love with him and desperate, letting her blindly stay with him is not only mean but could be seriously dangerous. It's time to stop turning a blind eye and hoping things will resolve themselves. It's long past that.