Anyway the point I am trying to make is that you can perfectly enjoy their relationship even though it is absolutely unhealthy. The messiness of if it all informs you a lot of things about the setting and the characters involved. Was it executed well? Eh not reallyyyy, as I wish Rinea had more chances to express her thoughts rather than being used as a plot device in order to humanize Berkut or more accurately- not be so underwritten cuz *cough Echoes has a misogyny problem.
The relationship between the two being unhealthy is not an indicator of bad writing (imho) because it communicates aspects of Berkut's character and how much being in Rigel has influenced him. The tragedy between Berkut and Rinea is how things never properly began for the two of them. Berkut was focused on being the next in line for the throne, meanwhile Rinea was living in her own fairy tale. The actual bad part of it is how little we see of Rinea's side of things by comparison which is yk... tied to the actual major issue of Echoes' writing (misogyny). It's a topic that has been talked about already, y'all know the drill. That aside, Rinea's passiveness does make sense, she is a noble from a minor house. As Rigel at this time values strength above all else, you would think that would apply to how people would get higher in rank as well. In Zofia, class mattered based on the fact whether you were a blueblood or not, Clive wanted Mycen in the Deliverence as he was both a former count and a war hero, therefore appealing to both to nobles AND commoners in the group. Comparitevely, in Rigel contribution and skill hold more leverage than a mere title. It's why Berkut is dragged for every single one of his failures and openly mocked by the faithful such as Nuibaba. He is supposed to inherit the throne, why is he fumbling? Therefore it would not be farfetched to say that Rinea's family is of lower aristocracy because it cannot contribute much for the country in terms of what the said country values. Berkut approached Rinea in the first place on a whim because he can do what he wants and nobody can really tell him no. He puts his position as the emperor's nephew front and center during their very first meeting. You can argue that Rinea not being firm with her distaste for violence and Berkut's more emotional outbursts were both due to her position and naivety. Plus, you can debate that Berkut being with Rinea at all is in line with his inferioty complex so going for a girl who is looked down upon in high society is because he can relate to her. Everything positive between them is as I had mentioned fairy tale esque, they dance as if nobody else exists in the world but them, Berkut would given her the entire world if he could. By propping her up, he would do the same for himself, at least mentally, not necessarily in the court. So it is simply sad that they never got to sort their issues and grow as people first before everything went totaly downhill. You can't say that he didn't truly love her, that is not how this works. I mean what ended breaking Berkut in the first place was when Rinea in his eyes "rejected" everything he built himself up to be. He really could have had anyone but he picked her and he wanted it to be her and only her by his side. And if you interpret his final moments as him hallucinating Rinea forgiving him then that is even more evidence as to what makes their tragedy interesting.