Do lists for this exist somewhere? Because with my choice of words I couldn't find any....

Otherwise I'd just start one but it would be great if there already were collections out there.

      ->**[Flowers](https://www.mangaupdates.com/series.html?id=4790)**  
      ->**[Okubyoumono ni I Love You](https://www.mangaupdates.com/series.html?id=111237)** 

Yeah, I know I can't think of more right now... I'd update in case I'd find more, probably in the comments, tho.
Anyway, Feel free to add loads more to it or link to other lists!! 😀

Personally I wouldn't have very strict criteria, except for the obvious from above 😉
- a close acquaintance of the love interest (or maybe also the protagonist)
- knows love interest longer, than future lover
- hopeless love for the mentioned friend (can be aware or oblivious to the love interest)
- preferrably an actual intervention/ relevance of the love triangle
(rather than just a short side note)

       -oh and if the story contained rather harsh/ critically seen aspects as rape or whatsoever it      might be nice to mention... though I guess it can be figured out in other ways, too, so as you like  🙂 

For now I can only think of Koi Nante Shinai! and Bukiyou Dakedo Daisuki sa (the friend has a separate story in chapter 5)
Try the 'unrequited love stays unrequited' tag~ (include the tag 'jealousy' if you want to).