When we talk about girls we discover things: Some girls agree with a lot of things. Some girls don't. Some girls choose to go out with their friends often. Some girls choose to be alone. Some girls love to shop, some love to save. Some choose who they're going to befriend with but some girls don't mind who they're with.
But when we talk about friendships, we also discover a lot of things: Friends share stories. Bestfriends share stories particularly personal ones. Friends shop together. Bestfriends shop together but they shop the same things once in a while. Friends don't have that enough guts to wear the same things from head to toe. Bestfriends have a lot. Friends care for their other friends. Bestfriends care for their friends, bestfriends and their bestfriends' families. It's good to have lots of friends who you call anytime but most of them just come and go. It's better to have a few close friends, probably a handful, who'll stay with you not just with your ups but, as well as, with your downs.
There are a lot of factors for keeping a friendship-- like being loyal, trustworthy, giving respect for each other, no pretentions (you just have to be the real you), and such. But the ultimate factor for that is to acknowledge God as the center of the relationship.