Looking for a one-shot h-manga that I saw years ago, and couldn't forget about. It was posted first on FAKKU a few months before everything turned subscription, and it went away with the site re-organization.
I'm hazy on a lot of the specifics, but it featured a boy and a girl having to share a room between them. Unfortunately the girl is shy (or something) so there's a curtain between them. He hears her masturbating, and she reaches a hand through the curtain as she does so, so they both do it while holding hands because she's too shy to show her face while they do it.
Nights go by and they ramp it up each night until they're blowing and fucking each other through the curtain, until they finally pull the curtain aside and do it face to face.
Ring any bells?