This is poorly written but I don't think the writer deserves too much flak outside of that. The story is good enough. It seems like a waste because it had a good premise.
I'm still going to read it til the end but yes, there's definitely a pacing and exposition issue. I feel like the story itself could've worked better if handled a different way. I don't know how exactly but not this way.
As an artist, I hate the idea of plagiarism but if Asami is telling the truth (which I think she is) then I see no problem. The only thing she'd be plagiarizing is the supposed incomplete song and she stopped herself from doing so. Granted, she's being rather bitchy. I hate this kind of plot twist when they break up with someone for the person's happiness. Ughhh. Makes me want a het ending for a second. But I'm pretty sure they'll get back together.