Sometimes you just like something so much because they're so cute that you don't have the heart to push them away whenever that thing loved you a lil too much ┗( T﹏T )┛(speaking from experiences)
Yuu actually shrugs it off as child play at first which I understand because everyone have those childhood crushes before and he just thinks Tsubaki is confused since they're close but ever since that annoying brat (the one that gave Tsubaki lewd ideas) appeared and started suggesting stuff to Tsubaki, Yuu started getting nervous because he didn't think that it'll escalate like that so now he doesn't know how to reject or put Tsubaki to a stop because he doesn't want to hurt his feelings because he might discourage him when it comes to love
Yuu is too complex and people misunderstand him which is too annoying tbh. ヽ(`Д´)ﾉ
Why the fuck are you not stopping that kid bruh wtf!! You are older be more mature AHGHHHHHHHHHHH.