[✓]My Fiancé is in Love with My Little Sister

[SPOILER]Known and probable Soleil and Sylvia's endings after FL dies

We can said they didn't have an "happy life" most of the time.
Life 1 : We know Soleil was killed by Al after the death of MC. He was crazy too.
Life 2 : MC died before Sylvia. Either her family tell her or not about it, Sylvia cannot die in peace. If she knows she will be sad because of what she said at their last meeting. If she didn't know, she will be sad to know MC didn't forgive her. Soleil will never be happy and probably regret his behavior toward MC.
Life 3 : We know Sylvia had a miscarriage from the shock of the suicide of MC. She probably never forgives herself. Even if Soleil is totally shameless in this timeline, he probably never able to really have Sylvia because of her trauma.
Life 4 : Difficult, this one. I don't think we have enough information about her situation and death to make hypotheses here.
Life 5 : Sylvia and Soleil starts a depression from guilt. Soleil go to war and die here even if he didn't need to since the battle was an easy one. Sylvia let herself die at home.
Life 6 : We don't have enough information apart from her car accident.
Life 7 (mother suicide): The father kill MC in the funeral (this is a bit unclear part for me. Not sure if he actually killed her or she died for some other reason. Still confused cuz of spoilers), I don't know if he felt guilt but Sylvia and Soleil will probably being shock by that. If they search about the answer MC didn't give, they will probably find who badly MC was treated and feel guilt. If they let it go, they could be together I guess, free of guilt since they know nothing.

Apart from 2 timelines, with the personality of Soleil and Sylvia we can say they will not be happy most of the time. Of courses, it's only hypotheses, but I think it's quite good.

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Source of the Spoiler :: Novel Updates Forum