Blessed handholding.
I feel like Tsumugi was a lot secretive because whatever she had to deal with, she probably didn't want to push it over to anyone. If she had called, told her circumstances, sure Midori might have tried to do something, like you know, talk to an adult, but she was never given the chance to.
For someone passive like Midori deciding to face Haruko with the truth must have been really hard. I'm glad she did it anyway without cutting any corners. Its always healthy clearing misunderstandings during cohabitation.