Well, to tack onto what you were saying Eissy- a lot of the UPG and PCPG I read about Jotnar in general explains that they tend to be very polygamous. They don't have the same kind of concepts about relationships where it's only two partners. I guess they tend to be a little more "open" in that regard.
However, I think within this specific story Skadi took the intamacy with Loki as Loki showing intent to be with her. But he up and left, without even being in any kind of relations with her, immediately afterwards. I think that's perhaps where the bitterness of the whole affair stems from. Keep in mind Skadi is also an ice-jotun, who tend to be a little less receptive to this kind of thing (in general) and can be possessive.
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Loki: Well, this has been pleasant. I'll be going now.
Skadi: Wait, what? You just got here. You're not staying?
Skadi: You don't care about me?
Skadi: How dare you!!