After A Love Ends, Another One Starts
I finished the title.
I know that. But the idea is that the two of them spent time together and got to know each other over the time she kept coming to hopefully run into the other girl. But their conversations at those times are awfully shallow, so we don't see them becoming anything but acquaintances and we need to take it on faith there's anything more between them.
I dunno, I see it as Wataya-san already knowing that her kouhai would reject her, making her open to love already by the time she met Araki-san, but yeah their conversations were a bit shallow