Goodness gracious, honestly this just seems like an emotional ticking time bomb waiting to go off. Well Ichika had plenty of chances of escaping, so I can't say I'm concerned for her anymore. So long as we're over the backstories.
I don't even remember anymore how this whole thing started, but I somehow still don't want to let go of this series...
You didn't miss much honestly.
But a recap in case you're interested:
Kawase (girl that mc likes) and her kissing friend saw what looked like Rei (Kawase's older sister) kissing Ichika (MC), which stirred up some drama and misunderstandings... So afterwards, Kissing friend decided to have a sleepover at her place and invited Kawase and Ichika (who only agreed because she wanted to avoid having Kawase and Kissing friend together by themselves, and somewhat interested in what tales they had). Kissing Friend (I know her name is Shiori, but I don't really care), accuses Ichika of seducing Rei, but they learned that the kiss didn't happen (I think it was like a light peck next to Ichika's mouth). So upon realizing that, Ichika asked why don't Kissing Friend just go out with Rei.
To which we have nearly 17-20 chapters of flashback that showed how Kissing Friend first hated Rei, but then fell for Rei, and then Rei and her started dating. But Kawase had a fit, so Rei broke up with her. So Kawase and Kissing friend started kissing each other for reasons, and this continued until Ichika discovered them and setting everything in motion.
Something along those lines anyway.