
Don't read if you don't want a spoiler...
She didn't want to marry the foriegn king just to be discarded later when he found a new woman that peeked his interest (like his current queen). I think she picked Regan because he was of the royal line so he couldn't be objected to, but his reputation is such that nobody would believe him over her. The problem is that he's obviously traumatized by his past (previous wives and nobles' treatment of him for being a bastard child) and has addiction problems . Ingrid isn't emotionally or mentally ready to handle it. The man came with serious baggage that he was more than upfront about, but she forced him into marriage anyway. Now that they are together she keeps acting like she shouldn't have to spend time together with him and try to break down those barriers. She just gets mad at him for not understanding her. He has tried multiple times to reach out and have her stay with him, but she's not getting it. He's an addict who has been surrounded by scummy and abusive people for a long time. It's going to take a lot of uncomfortable communication and serious dedication to get through it all, it can't all be on him.

Thank you for your answer, I can appreciate the story better now that I know more about her motives. The fact that they were explained way later in the story quite reduce our ability to empathize with her first.
I am a bit more advanced in the story and I agree with you that Ingrid seems to not understand the ML. I feel like she doesn’t see the full picture, of him and all his issues.
So I’m just at chapter 8 and for now it’s a bit hard to continue because the story premise doesn’t make total sense : whether it’s because of flaws or lack of further explanations.
The main reason why Ingrid doesn’t want to be married to the foreign king is because she doesn’t want to leave her country. ( Her brother assumes that her actual reasons are that the king is much older and he is not that nice - but Inga doesn't talk about that. So let put these motives to the side. )
When I saw her fighting to avoid this mariage to the point of tarnishing her reputation, I thought there would be a big reason : like maybe her life would be endangered in the foreign kingdom ? But no... In a letter, she said « a flower that is plucked from the soil of it’s beloved homeland will wither up from despair » - which is quite overdramatic.
Moreover because she believes she will live more happily in her native country, she publicly pursues the ML, which for sure is ruining her reputation (because he is a famous fuckboy). Anyway, what is the logical consequence of having a tarnished reputation ? -> you become outcasted and looked down by the others nobles, despised by members of your family.. and all of that, in YOUR country, where you think you will be happier, right ?? With that in mind, why does she think it’s better than her leaving ? I don’t get the logic ╥﹏╥ the only reason why it would make sense is if she is super patriotic or ethnocentric. But to the extent of making that much hardships for herself... it’s kinda illogic too.
Among the hardships, there is obviously the difficult cohabitation between her and ML, but at least she is aware of that so I didn’t mention it until now.