Looking for doujinshi. From what I remember it went something like this - there are two girls. Girl A is petite and likes girl B who is a tall and muscular tomboy (maybe had short hair). Girl B was part of some sports club, most likely basketball but could be some other. Anyway girl B keeps disappearing during recess or after school, girl A gets curious and after following her finds out that girl B is meeting with coach / teacher. There's only one scene where girl A watches them having sex through the door and masturbates repeating something like "don't lose girl B" and is distraught at the sight. There's little backstory to how girl B started meeting the guy, but the scene is when it has been clearly happening for a while and girl B is at the breaking point and loses to dick. It should've been easy to find, but I think it was a work from a new artist / possibly not tagged thoroughly. Any help appreciated.

Nvm found it - 誰にも負けない私だけの王子様 by えこひいき