Why is it customary for a heterosexual woman to refer to her heterosexual female friend as a "girlfriend",but not the case for a heterosexual man and his male buddy to call one another "boyfriends"? How did our language evolve this way,and is it similar in other languages throughout the world?
I think the following extract offers an interesting point of view on the subject:
A Lexical Beef: ‘Boyfriend’ and ‘Girlfriend.
Etymology Online dates the term “boyfriend,” meaning “woman’s paramour,” to 1909. However, the term has an earlier platonic sense. The first use I managed to find in Google Books, from an obscure 1850 publication titled Friends’ review: a religious, literary and miscellaneous journal, describes the friend of a young man, not the lover of a young woman:
Though daily occupied with his drudgery as a farm servant, he began to instruct himself in Latin and Greek. A boy friend lent him several books necessary in these studies…
Girlfriend seems to have had a similar trajectory, beginning as a term for a young female friend, only taking on romantic connotations after the conversion of boyfriend. Intriguingly, the original sense of girlfriend is still alive and kicking, as one can hear in phrases like, “I’m going to spend some time with my girlfriends this weekend.” I can’t say for sure why the platonic meaning of boyfriend didn’t also survive. Perhaps some consider it un-masculine to refer to your drinking buddies the same way their girlfriends do?