My fanfic experience leaves me very reluctant to assume anything about a character's orientation. The thing about LGBT+ representation is that it isn't automatically visible in the way race or gender is, so unless it is brought up in the course of the story, it may very well go unnoticed, unless every character's two lines of dialogue include 'hi, my orientation is X'.
Personally, I'm not fond of close bonds automatically assumed to be romantic, as fandom so often does. They could be, and that's fine, but if 'cares about' is conflated with 'in love with' too often, the relationship usually becomes less interesting to me.