Feels way too random and forced.
I... agree, actually. It's like, two-thirds into the chapter, the story made a brutal turn without signalling.
We had the pressure-weak MC, her inner conflicts, her feelings of having let down her parents and brother, then the ridiculous teacher, the shady deal, the neet girl who seems to need help, then suddenly blackmail, being forced to submit under threat, now the former neet girl will get to do ecchi things to her every day...
Too many ideas thrown together, not enough development on any of them.