1. FMC kinda cried while leaving with the douche, so did she do it to save MC?
2. Who was that douche, i don't know since i just browsed through some raws
3. Why FMC changed her hair colour?
4. There seems to be a sequel, is it connected it any way?

The childhood friend trying to get the mc and others out of the weird prison losing their virginity. THE ENDING The childhood friend got kiss by a BASTARD in front of the MC . So the manga is over.. The Childhood friend taken by that DOUCHE and staying forever locked away in that HELL WORLD NTR

I skimmed through the chapters and I think the only important chapters (the ones with the main heroine) are ch. 43-46 (you can read ch. 1-50 translated on a certain other manga website) and the last chapter that's only released as a raw, ch. 104 (on yet another website), which is the cliffhanger NTR part (yes, it seems the white hair girl is the main heroine with previously black hair and she's been brainwashed(?) or something). Seeing how it ends, I really don't think this is worth wasting your time reading 104 chapters of (even if they are short chapters).

Just the fact that this is a "manga" and not a hentai doujin, I really don't think the main heroine is going to have sex with the NTR guy (even if he did say he's going to) as a lot of people are speculating to happen, but the balls of this author to blueball readers for 104 chapters and then introduce NTR is fucking baffling. I honestly don't care even if the sequel reveals a happier ending, I wouldn't waste any more time reading any of this author's works.

the cover girl got taken by force

Some men, transform due to having sex... ok, then cockblock sex, to get information...then transferred to fantasy island, cultural festival arc with shounen action...and the other inmate's real targets are men...contest for a d*ck...and another cock block, for telling a crime...and then a guy immune to the virus due to a super drug...wait.. the MC's love interest was brainwashed? and then... the end.. woah