
I haven’t been that far in the novel so I can just provide snippets
•Jieun was the one who turned back time (not sure if this is true) so she could get revenge on Aristia
•On the past life, Ruve “went crazy” over missing Aristia, 4 years after her execution. This ultimately destroyed his relationship with Jieun which is why she wanted to go back on time.
•Aristia backed down from a competition to be Empress (against Jieun) so that she could become the House Monique’s heir.
•Ruve outright rejected Aristia’s blood oath (oath to pledge loyalty to the emperor) because he doesn’t want her to become the head of the Monique family cause it prevents her from becoming empress.
•Ruve and Aristia’s first kiss was a french kiss.
•Not sure if it’s true, but someone in the comment said that Ruve and Aristia lived happily, and Jieun got exiled.

Spoilers from what I read on a spoiler chain
Juen wants revenge on Duke Zena or the prince I forgot. The reason is that when Tia died she was often compared to her (gaining an inferiority complex) and the prince was drugged. So he never loved Jiuen and loved Artisia. He was sad when she was dead and Jiuen ultimately died by assassination. God also gave her a second chance like Tia. She doesn’t want to hurt Tia. As in fact when Tia gets poisoned (by Duke Zena) Jieun does something as a child of god (I forgot what it was) and saves her. In the end Jieun goes to a different country and lives happily. She and Tia aren’t friends but they have a respect for each other.

This is everything explained
http://www.mangago.zone/home/mangatopic/5175109/

https://wuxiaworld.site/novel/the-abandoned-imperial-concubine/chapter-135 (starts from when Jieun arrived)
Spoilers anyone?