BF can stand for boyfriend and best friend, although a lot of people use BFF for friend. To have a best friend forever to me means you need to have had the best friend for most of your lifetime and consider them until old age. Maybe I'm wrong…I often times am. My opinion remains.
Then there are the best friends that are BF interchangeably. They start out as one and morph to the other and vice versa. I grew up having a best guy friend that never morphed into the latter, but there were feelings there at one point that I chose to act on. Did he feel the same way? I'll never know, and I never asked. Maybe I was just scared, but I'd like to think it was to try to keep our friendship in tact as well. Often at a young age it seems that the interchangeable means the end of one part especially if the love dies; it's hard to keep the other. It sucks. Maybe the foundation itself was never strong enough to survive the set backs. I don't know.
Why then in movies, television, and books do we try hard to make it be interchangeable and we try to always make it work out. Is it a fairytale mentality? Is it that we all secretly want that friend you grow up with that turns out to be your magic soul mate? Perhaps. It also tends to lend itself to the notion that look beyond what you see and go for the unknown. Taking chances makes life better (mostly). It can also lead to extra drama and emotion to grasp the reader/watcher. You root for them, regardless of similar experiences or not. Maybe, you wished you had that guy friend that was your best friend, but yet, your best friend was the girl. Now that would change it up somewhat; or maybe not. You would still have all the crazy attached to the interchangeable.
Do you add this dynamic to your books/scripts? If so do you like the characters to work out? If not, do you keep them friends? Can you remain friends after changing it up…? I'd like to think so…but that's just my human nature wanting the best outcome and the fairy tale friendships/endings.