Spoilers
From my understanding, we go through a couple of Illya’s lives. All end tragically (except the “current present one”). I can’t remember the exact specifics, but the two that made me cry out the most was when she ran away in her fourth or fifth life and when Sylvia had the fiancé’s baby.
She ran away, got captured by human traffickers, and was sold into brothels. She slowly lost her life and at the end, Al finds her and brings her home only for the ex-fiance to be all like “I’m glad you ran away. I get to live with the love of my life” while Illya is dying. She, of course, dies.
In the other one, Sylvia and the fiance had a literal affair. Sylvia got pregnant despite Illya being married and basically controlled the house, acting like the Marchioness. Illya gets locked in her room and decides to tie a rope and ends herself. Little did she know, Crow visited and was the reason her corpse was discovered. All the servants ignored the body and only cared for Sylvia, who just lost her baby.
We get a little into Crow’s backstory and how he eventually ceased to exist as a “human”. This causes him to lose his love (yes, he loved someone else. But they moved on when Crow was “thanos’d”). He found Illya in one world and kept traveling to different worlds where Illya exist and tried to save her.
In the current-present time, he manages to save Illya from dying after Illya sacrificed herself so that Sylvia can live and be loved.
TLDR: Illya and Crow are tragic. Fuck the fiance and Sylvabitch

Sry but what were the spoilers so far?