Responses
I think the chapter implied that the reason for his purity wasn't just his lack of female experience. His dad isn't around, so he couldn't ask him questions, and he didn't hang out with other boys. Moreover, he even said that he skipped health class, so he doesn't even know the basics of sexual puberty.
I like your theory more.
I like the plot, and the characters.
On the other hand, I feel a bit offended that because the boy refused to make a single contact with the opposite gender, he automatically knows nothing about sexual things.
(Technically the manga is treating women as the origin of sexual desires or sexual objects)
I may be exaggerating it, but I would have liked something more believable for his absolute purity.
(Not to mention, I'm not a fan of the yaois who are gay because of the lack of girls)