
This might be right to a certain extent, but in her dreams her future self never remarried and refused to do so. Nor did she have any kids. Also, her future self in her dreams wasn't aware that the Iron King and Kuhn were partners (the only reason she found them together and met Kuhn earlier than presumably she was supposed to in the future was because of her dreams) so maybe she found it out in an unfortunate way.
I saw some spoilers, though it's a bit foggy
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there was also another woman involved later on with Kuhn, but only in her dreams so not in the current timeline. Maybe that could have been the cause.
Either way, the story is very interesting and I'm excited to learn more (▰˘◡˘▰)

I read spoilers that, this girl named Fatima was Kuhn's lover in the past life. She is from his territory (the desert), kuhn and her fell in love. But because of some diseases she died. And in the past life, kuhn was forced(i am not sure) to marry Seinna to hold her down from the throne.
This is why they had bitter relationship in their past life.
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Also when Seinna learns that another girl was involved in his past life, she feels extreme guilty that she stole someone else's place. (though kuhn is whipped for our silver king in this life)
I love how we're learning the future together with her. This is a refreshing take on the reincarnation plots.
So I'm guessing, she marries Kuhn after the iron king is crowned emperor. However, the iron king dies so she had to divorce him and marry one of the 6 families to produce an demi-god heir.