The point of having a term like YF is to enable us to differentiate between all the boys we know and the one (if any) whom we have a special relationship with.

I don't see the need to differentiate like this. Is the boy Cat knows young? Yes. Is the boy his friend? Yes. Ergo: Young Friend.

Also, as BLs, we have so many constraints around our friendships -- from parents or society or whatever. Just because a BL might only be able to see a YF for a very brief period of time, and only in a specific context, does not necessarily mean the friendship is any less important or meaningful to either or both of the parties.

Blessings,
Rainboy