This is what I know from spoilers:
What Ines believes to be her first life where she was miserable with Oscar is actually her second life. In her real first life, she was happily married with Carcel but she died due to an illness. Oscar remembers that very first life and since he’s always been jealous of Carcel, he married Ines just so Carcel wouldn’t have her. That’s why she said that Oscar r*ped her everytime they exchanged a glance. Ines and Carcel don’t remember their real first life but since Oscar did, it triggered him every time.
Also, in the current timeline, Oscar will hire assassins to Kill Carcel because he’s always wanted to get Ines again. Carcel won’t tell Ines that he’s constantly fending off killers who are after his life though.
Spoilers
Actually, it’s more complicated than that. Oscar always wanted Ines for her pedigree. She’s the noblest woman of their age in the crème de la crème of nobles. However, Ines chose Carcel to marry instead of Oscar. The problem was, Ines was unknowingly being poisoned by a envious bitch and that’s how she got sick as a teenager and eventually develops a terminal illness.
Ines and Carcel both died at the same time in that timeline. After their deaths, Luciano did a rebellion and put the emperor illegitimate son on the throne. The public supported this move and Oscar was executed. So Oscar’s hates Luciano since the first life. He was given a chance to live again just like Ines and Carcel and chose to receive memories in the next life he was granted since he died an unfated death like Ines and Carcel. Oscar used his memories of the previous life to torment both Carcel and Ines who knew nothing. He also tried to take out his revenge towards Luciano and his jealousy of Carcel and his vengeance for Ines not choosing him on all three. That’s how all the tragedies began again. It doesn’t help that Ines made wishes that were against her fate. This is how complicated this story is.
Spoilers
He does eventually remember on his own. His memory was triggered by an assassination attempt on his life. Then he began to receive more memories. Eventually, after the end of the main story, he receives the entire memory of his first life with Ines. So he remembers everything. Their entire life from the time they were engaged at 6 or 7 to the time they died at 28 or so. Then their wishes in the afterlife.
Carcel gave the gun to Oscar to give to Ines. Luciano gave the bullet. She used the bullet and gun to kill herself. She thought Oscar gave her the gun and wanted to use the gun to spite him but it's was Carcel's gun that he treasured given by his grandfather. The bullet that Luciano gave her was meant to use to kill Oscar but she killed herself instead bc she didn't want her brother to be punished. Everyone's saying her brother should've done this and that but they don't even know that Ines knew her brother was going to stage a rebellion for her and she didn't want him to be punish for it so she killed herself. She didn't kill herself bc of what Oscar did or trauma. She did it to protect her brother who she love.
SOME ONE PLS SPOIL ME