what annoys me the most in those "dating == end the manga" is that the author assumes a relationship is a finished product, something static that you must achieve, instead of a whole process. After they confess and start dating, they need to deal with SO MUCH MORE things than before, their personality clashes and differences, their insecurities and flaws, the creation of a new routine, new friendships, the steps of intimacy... So much to be explored, and many authors just ignore all of that and go straight to "in the final chapter, confession. Afterwards, is afterwards". Or, almost as worse, they go to the "love rival/enemy" trope. It's almost as if those authors never experienced a real relationship before.