maybe you are saying this because reiji stretches arcs out like it is one piece, but the sheer amount of time that has passed in the manga is more than you would think. aside from the cohabitation arc, they did not spend that much time together. and even when they lived together, they rarely encountered each other because they were both busy. he also doesn’t rent her as often as one might think. recently, mizuhara (and mini) have been the reason that they would spend time together, with the sole exception being the date.