"My best friend had taken my boyfriend."
Translation:Min bästa vän hade tagit min kille.
Perhaps I misunderstood, but I thought that pojkvän and kille were not synonyms. In that pojkvän referred exclusively to a romantic relationship, and kille would just be a guy, who is a friend.
I realise this is a late reply, but in case somebody else enters the thread and is wondering: you can also use kille for boyfriend colloquially - but not pojkvän for guy. The latter is, as you say, exclusively for a romantic relationship. Also, the same holds true for tjej / flickvän (girl / girlfriend).
It doesn't feel fair to penalise users with a wrong answer for not selecting both of those.
Probably not, no, since one is actively taught and one just generally accepted as an alternate translation. But Duolingo chooses words for multiple-choice questions by itself, and we have zero say over how it does so.
They mean the same, but the -e ending on adjectives is reserved for actual male people. It's always OK to write -a instead.
It's rarely used nowadays, and the translation doesn't mean an explicitly female friend.