I used to study Danish before and I really like the fact that they have a word, "kaereste", which can mean either girlfriend or boyfriend
Same in Norwegian (kjæreste). But there's also a Norwegian word for girlfriend that means a platonic female friend: venninne.
Is there a neutral term? Like romantic partner, signifigant other (and for marrige, something like spouse), etc...
Is this in the romantic sense of the word, or can it mean female friend too?
I guess you'd only say "vän"...
In which of the two cases?
flickvän specifically means in the romantic sense. You can call a female friend either just vän, or tjejkompis (the latter is more colloquial).
Could you say hon är min flickvän inte. Im used to putting inte later on in sentences
No, that doesn't work.
It's like saying "she is my girlfriend not".
hon är min flickvän ... INTE!"
But I wish she was...