Well, the MC is clearly not a reliable narrator. She's so obsessed with Marie that it's clouding her judgement in everything.
This. I like how you can tell how deep this girl's love delusion goes with her endless narration about what a good and perfect woman Marie is when clearly, that's not the case. There is no morally good woman who would tell her cheating partner's kid that her mom is also in an affair (which, she didn't show any proof nor someone in her place should tell the kid this information), say Sumire was being jealous of Makoto without taking their relationship into consideration or get into the affair with an older man who has a minor daughter in the first place. Makoto was also so blind in love that she put all the blame for kicking her out of the house on her father without taking what Marie said about this matter into account. Like yes, the father initiated the idea but Marie was agreeing and onto it as well. It's just that she wanted Makoto to live alone rather than living with her mother.
