Otoko Girai na Bijin Shimai wo Namae mo Tsugezu ni Tasuketara Ittai Dounaru? - Ch. 16

[Jampolo]

I think Crimson was asking how the 3 are virgin to each other with how much they push MC from even before they actually got together, not how the girls kept it with how thirsty they are.
Simple answers, the girls developed hate and distrust towards males as they were molested and seen as nothing but a piece of meat from a young age, lost their father so they couldn't count on him for protection or get used to a male presence, MC saving them withotu asking anything in reward and if anything trying to hide it to avoid making them feel like they owed him anything made them understand he is a rare good guy, of course being childhood friends helped.
For hoow they stil ldind't do it, even simpler, MC wants to take it nice and slow, get to it "naturally" like he have seen in novels and TV, not the the hentai approach, he tried to avoid making bonds with other people after losing his parents, so it takes a while to open up.
All 3 wanted someone to love, but are a bit weird in how to express it after bottling it up for so long.
MC delayed it through exams, but his walls are crumbling.

And from What I've read in the past

Spoiler: novel spoiler

MC does do it with them, and their mother too, but is possible that the manga decided to avoid doing that too fast, is possible the spoilers weren't correct, but it certainly feels like is going that way

The manga is taking a sensible approach if that's the case

 

[SSRBReader]

Man, that was fast—introducing his ex already.

I hope the MC doesn’t entertain her. I mean, she’s an ex for a reason, right? The MC already has two diamonds in his hands.

 

[JethroBodine]

"This fucking bitch here..."

She talking about Hayato's cold gaze but she ain't so bad herself.

 

[Kalbiaczek]

People will call him dense and stupid for being uncomfortable about these girls literally masturbating themselves every single time that are with him