Yeah that also confused me. It might have been a translation error but the kanji for shinyuu (しんゆう - best/close friend) is "親友" while for shinjuu (しんじゅう - double/lover's suicide) is "心中" . It would be hard to get them mixed up haha (also since they're usually written in kanji and not kana.) But i don't have the japanese raws so I can't really confirm what they meant.
Honestly I feel like the whole manga had a lot of translation errors / inaccuracies especially during the Yoyogi-senpai scenes, but it can't be helped since translation is difficult hahaha. I do wish someone would fix the errors though because this manga is beautiful. (╹ ◡ ╹)
So I was quite confused in chapter 5. I mean they wrote "shinyuu" what is close friend/best friend, but I think they actually meant "shinjuu" what is double suicide, because you can't commit shinyuu, right? lol
Tell me if I'm wrong though lol