I dislike the "childhood friends, but one forgot and the other is mad about it to an irrational point" trope. I disliked it in Canno's manga, I dislike it here too. It feels petty and forced.
It took me way to long to remember which specific ship you're talking about, and I feel kinda ashamed for forgetting them, since they were like my 4th or 5th fav ship from AnoKiss. I probably should re-read the manga when I have the time.
btw, I know the source links to twitter, but there's an r-18 album on pixiv containing this and 12 other images. all the possible two-person season 1 liella ships get featured at least once, and there's also a RenKanoChii image and an image where all the other 4 go down on Kanon. https://www.pixiv.net/en/artworks/103016154