I like this description...

"What characterizes a close, meaningful relationship?"

(1) Friends spend time together, almost every day.
(I don't think this necessarily means in person)

(2) They interact freely, easily, and honestly.
They feel safe enough to "be themselves,"
sharing their private feelings and experiences,
both their successes and their failures.

(3) To last, both must get more satisfaction than hassle from the relationship.
Both must feel they are getting a fair deal. Both must strive to make the other happy.

(4) There is a code of ethics between friends based on loyalty and trust. Friends are tolerant of and devoted to each other; they are fair, emotionally supportive, and willing to help whenever needed."

"Good advice is to take your time making a friend. It takes, on average, 3 years to become "best friends."