Honestly, I feel like the author's setting up for her sister's relationship with Yuu being the source of conflict going forward more than the lack of resolution with the (ex?)-boyfriend, considering how much of an afterthought the latter seems to be at the moment.
I was waiting to see when the next shoe was gonna drop cuz the past few chapters have been way too wholesome but I was not expecting this twist with Nanase's friend lmfao