Clarification
There’s no relic. This story is more on the historical side with some element of fantasy which is loosely based on Catholic belief in purgatory. Carcel and Ines were indeed married in the original timeline but they died in their late 20s due to unfated deaths. The crown prince also died an unfated death. Anyone who dies an unfated death gets a chance to live again when they enter something like purgatory. With the chance to live again to correct their lives according to fate, the person gets to make wishes.
The crown prince wished that he would keep his memories of the original life. Since he retained his memories, he was able to do what most regressed FLs do. Manipulate fate and take advantage of others with his previous knowledge. As such, he approached Ines as a little girl and acted nice to her. He treated her well and basically wooed her into thinking he’s a good person. Ines usually falls for people who treat her nice. That seems to be the common denominator with her. Therefore, she fell for the prince enough to be won over by him.
Another thing is the crown prince approached her very early when Carcel was a little boy since he’s the same age as Ines. Carcel always begins to like Ines around 7 years old. Ines was engaged to the crown prince before Carcel even turned 7 years old. So there was no way he could do anything about it when Ines was already engaged. Besides, Ines is the one who always chooses the men in her life. She chose Carcel twice. First in the original life and the second time in this last life. Still, the person Ines is fated to be with has always been Carcel because had their lives not been destroyed in the original timeline by a woman who hated Ines, they would have lived out their fated happy life. This final timeline is to correct their fate. That’s why apart from each other, Ines lived devastating lives and Carcel always died unfated deaths on the battlefield. Neither has lived a long life up until now.
if the crown prince chooses to recall the memories of his original life, what about Ines n Carcel??
Spoilers
Ines and Carcel chose to wish for each other’s happiness. Crown prince chose to wish for his own revenge because he died an unfated death in humiliation. Therefore he wanted a chance to get what he wants in the new life. That included getting Ines who is the highest ranking girl they’re age. He also always coveted her but she was Carcel’s wife. Carcel never let him get near his wife. Carcel even challenged one of the crown prince’s guards to a duel because crown prince tried to mess with his wife. Carcel killed the guard in a duel. So, in a way, all of Ines’s misery started with the crown prince as the root cause.
I'm pretty sure I read that carcel and ines were together but somehow the crown prince got his hands on a relic to go back in time and snatch her away from Carcel. So pretty much the crown prince is the cause of all her misery in all the lives she lived until now. Carcel and Ines were always fated to be together. I wonder when she'll recall her first life though.