You're right, Ayeon definitely needs to change, and she's extremely manipulative. If there's any chance of her actually getting with Sol, she'll have to seriously change and make up with So-i.
Also, I love So-i's character development too, she's even face-to-face standing up to Ayeon now. The main reason we just talk about shipping is that we don't wanna focus on all the bad stuff and how gut-wrenching it is to watch two girls with such chemistry, but such a painfully complicated relationship, fall apart

People don't seem to realize that Ayeon is projecting onto So-i. She's looking down on and telling So-i not to look at Sol as a savior. However, who is the one who wants to get close to Sol because Sol fixes their problems?Who is the one who doesn't care about the other person's feelings? Who is the one acting out of their self interests? Ayeon is.
Not to mention Ayeon is horribly manipulative. Her observant nature allows her to act quickly. She took advantage of Sol's kind-heartedness and made Sol symathetic towards her. She's just as wealthy and privilaged as So-i, yet she purposefully brings up the conflict with her parents/family so Sol will feel bad for her. She doesn't respect Sol's wishes and sticks to Sol knowing that Sol can't refuse people. She makes suggestions in her favor, not necesarily what's best for Sol. Not to mention, she's so malicious!! The things she did to So-i only ended two years ago because So-i stopped going to school!
So-i has been changing as a person. She has been gaining more confidence and is trying to deal with her sensitivity through self reflection, therapy, and honesty with her friends. She was even willing to talk things out with her abuser for Sol's sake, whereas Ayeon doesn't care about what Sol actually wants. So-i also doesn't just hang out with Sol, and we can see her relationship with other people develop, like with Dayeon.
It can be frustrating reading some of the comments because this is a great story, but some people only talk about how two girls are definitely in love. I get it, shipping is fun. There were some scenes I was oooh-ing at. I was hopeful that Ayeon would try to change. But given the way the story is going, I think it might be better to cut off this relationship.
Also, there's so much to this story than just the relationships! What about the perception of art? The struggles of being a student? Finding one's self? Reconciliation? What it means to be a friend?
It's just annoying how there's so many aspects to this story but a good chunk of the comments just cares about shipping two girls. Since most interactions with Ayeon come from Sol's perspective, it seems like Ayeon's manipulation is working on some of the readers as well.