ImSenjou ; You are talking about romantical feelings ? right? , because my interpretation (which differs from DS and Defens,) she has "platonic" feelings for MC only in the path were you are a totally selfish prick, she is cold, I also tend to see the Templars as neutral (I don't trust them at all) I also don't see the Elves as enemys, they are protecting their race from danger, Medb is not hostile at all, MC has to earn her respect, so she is bitchy, and hard, but Elves, don't lie, so from that I trust them, an Elf will tell you straight away that he hates you or don't trust you, despite being able to manipulate you, and not being manipulated by you (Jason complained about that)
My point about Kaija, is what did she feel about him before the revelation?
How she acts towards the protagonist depends on how the protagonist acts towards her, and I think that's wrong, they've known each other for years, they dated and lived together, what's her opinion towards him?
If you are interested in her, then she is interested in you, but if you are not interested in her, she is not interested in you either, and that is what I think is wrong, I think she should already have an opinion formed by the years spent together.
If she didn't love him, that's okay, there's no point in starting to love him now; and if she loved him, that feeling won't disappear like that, she should still have those feelings for him, and try to repair their relationship, even if he tries to avoid it.
The protagonist's sister mentions that she feels that Kaija really loves him (Something like that, I don't remember the dialogue), but Kaija doesn't show it, so I wanted to see her feel jealous or something similar, when she sees the protagonist with someone else, but I think she will not only not care, but be happy for him for moving on.
Anyway, that's what I think.