The expanded first chapter (I redid it with 3 extra pages I found on the author's twitter) says clearly that they are not dating, but they're childhood friends. If it stays true to the childhood friend trope, they probably have seen each other naked plenty of times, bathing together, etc, but probably not recently. I found something funny on the twitter page where the author says "作品内の二人のやりとりは特殊な関係性でのみ許されるものです。決して真似しないでください" or "The exchange between the two characters in this work is only allowable for those in a special relationship. Never imitate it, please." So he knows that their... banter is pretty extreme.
The pattern generally has been so far: she starts some shit, he doubles down, and she gets embarrassed. 99/100, he'd get in trouble irl, but I guess they do have a "special relationship."
This manga has been serialized as free manga on Comic Walker (https://comic-walker.com/contents/detail/KDCW_MF00000150010000_68/) on a biweekly release schedule. So far, 2 chapters have been released and it's a mix of Pixiv and new content. Chapter 1 abandoned the expanded Pixiv storyline, and i think CW content will generally tone down the Pixiv content, and some of the Pixiv content will serve as a springboard to CW content. I don't have any plan to scanlate the CW content at this time since it'd mostly likely be duplicative, but if a tankoubon is released, then I'll probably do it as a new title (like how Yancha Gyaru Anjou-san got split as web and print release titles).