bestfriend or love?

all of us certainly have friends.

there are our friends and our bestfriends.

we can have friends in opposite sex.

when we are being with same sex, we can tell anything about us,

we can share, we are feel free to do anything.

but, when we are being with opposite sex, usually, we just chat and share about our boyfriend or girlfriend.

when we find out our bestfriends, there will be a woman or a man.

between woman and woman or between man and man,

it's possible to maintain the friendship.

but, friendship between woman and man, it's hard to maintain.

why?

in my opinion, between man and woman there's a will to downed on each other because of physical

attraction or other reason.

so, do you think that good friend (opposite sex) can also be sweetheart?