Agreed on all points about this not turning into some horror-fest of Stepford Smiler Waifu Rape. While it's interesting in small doses, it would have become something horribly long and drawn out in this scenario. Mainly because the only person who would have cared enough to do something about it (Finn) would not have heard about it - possibly even until it was too late to save her. I've seen a few stories that end like that - where the former lover was so far gone that the only thing to do was to either place her in a psych ward or put her out of her misery.
I suspect this thing goes a lot deeper than some think because Vigo (The "Butler") mentioned something about a "Great Mission" and implied that Jair's Father, the Prime Minister, is at the head of it.
What I'm curious about is that I'm getting the sense that Alfine is more than just a plaything for Jair here. Granted, Vigo said to the monster-knights to kill her, but that seems like it was a last resort kind of thing. Why is she so important that Vigo needed to help Jair get her? I can only imagine that she's a critical piece in this "Great Mission".
And given the nature of those knights? That they may be some kind of inhuman/artificial creation? I somehow suspect that whether she's taken dead or alive doesn't matter - that they can use her for whatever role is intended for her, even if they have to reanimate her corpse. (Although she won't be much fun for Jair in that state - that part is probably just a nice bonus for him... unless he's all "HA-HA-HA JOKES ON YOU I'M INTO THAT SHIT!")
I also suspect from the way they were talking about a timeframe that there was something else at play - that they had a means of brainwashing her. I suspect that it was something they were putting into her food because they were really concerned ab out her eating her meals. And it was only a matter of time until it she had enough of whatever it was in her system to take effect and make her susceptible to their suggestions. Her actual health is only secondary to the matter - like it's better for her to be in good physical health so she can better carry out the role she is supposed to play. Not exactly necessary, just better. (See: earlier suspicions about her being useful, dead or alive.)
While it will be interesting to see this plot unraveled and uncovered, also interesting will be to see her finally catch up with Finn.... Of course, in order to get back into Finn's good graces, she's going to have to make a lot of concessions. There's gonna be a lot of crow and humble pie she's gonna have to eat, here. But given what she said about no longer caring about her titles as a Sword Saint and a Noble? I think she'll be able to swallow that pride of hers.
Which just leaves how things are going to go between her and Noelia. This is gonna depend largely on what direction the author/manga-ka intends to take things. But given what's going on in the background with this "Great Mission"? I suspect that there will be rewards and accolades enough that no one is gonna bat an eyelash at Finn having more than one wife.