I guess they could of indicated it, but honestly, I don't even look at this read like that. The main theme in this book is mainly relying on your friends and family and about game plans on how to exist difficult situations, rumors and relationships.
The MC are cousins, that don't realise their feelings before at least chapter 50 and this element was kind of a background element and is meant to become predominant later, as a surprise for the reader, and even then, it remains a platonic relationship, except for a small kiss. Personnaly I think there was enormous hints since the beginning, just looking at how obsessed they are about each others mouvements.
Sigh
Wish the incest tag was here. Wouldn’t have to bother with this since I’m Not a fan of incest.