Is "koramiko" definitely always "boyfriend", despite "amiko" being gender-indeterminate?
I know the word "koramikino" exists if one wants to specify a female girlfriend of the feminine gender, but what I'm asking about here is the flexibility of "koramiko".
Different languages have different rules regards this sort of situation, so I'm wondering as to Esperanto's.
Of course, from a descriptivist rather than prescriptivist point of view, even if Esperanto does have strict gender rules in this regard, I wouldn't be surprised to find them being ignored at will amongst at least certain more liberal demographics.
It is in fact a neutral word, because, as you said, amiko is neutral. I think people sometimes believe it is male because many languages diferentiate between boyfriend and girlfriend, and most esperantist too. Personally, I try to refer to my girlfriend as "koramiko" buy it still sounds weird.
I personally prefer to use "koramiko" as a gender neutral term, as it is more inclusive towards people that do not fit into binary gender identities. I typed "lover" as the English translation, and it was accepted (I imagine another gender neutral term like "partner" would also be a valid response).
With that word is one of moments when it is important to disambiguate and say the actual gender, especially because in the Esperanto community I think no one would be surprised about possible LGBT and it may be much more missleading than in other contexts (but in the other hand no one cares because there is a lot of tolerance).
In conclusion, say the accurate gender if you want to avoid unimportant confusions.