Wait is that a spoiler?
I am pretty sure she was meant to be his soulmate due to the fact that she felt such love for him that the god of that world drew her there to see if her love for him could change his fate. Now unless you are talking about the twin sister that is supposed to be with the prince, what you just wrote doesn't make much sense.
It isnt (well i hope not) its just a plot that sometimes is typical in romance stories so i just theorised
well maybe you could be right
I'm pretty sure that if you read it from the beginning you'll notice that the FL is the twin sister to the heroin of the story. The FL's twin sister starts out being kind and gentle to the ML but falls in love with the Prince, who is her soulmate. This causes the ML to lose it and he turns to the dark side, and sells his soul. The FL reads the original story, and feels such comparison and sorrow for the ML that wishes that she could save him and show him true love. In fact she loves him so deeply she dreams about him, and her heart aches when he dies in the story. I think the god of the story's world felt that and pulled her I to the book, creating a twin sister for the heroin, and allowing the FL the chance to show her love for the ML. Her crest has no Mach as of yet. I think that when she finally wins over the ML he will show a creat to match hers. Especially since the god of that world said that bore the God's Crest and that they hoped she could do what she set out to do, which was to show the ML that he was truly loved, and deserved to be loved. But that's all my speculation.
the guy is like still in denial about his feelings and the girl keeps liking him, even though she has a soulmate, but when the girl realise his other personality (the shitty one) she will be like thinking oh what i read was all one sided and then when she decides to just follow her path with her soulmate,the guy gets jealous and he realise he likes her and etc.