Best friends?

Best friends?
What does this mean.
Its something that cannot be seen.
Caring, loving and always there,
No hate, regret or any despair.
Sharing secrets that can never be told,
Going through life hot or cold.
Best friends?
Either family or friends,
But someone you trust till the end.
Knows everything about you,
And how it can be solved.
Even the slightest frown and they will come running.
Best friends?
Everything i have just said and much more.