People tend to blind themselves when it comes to friendship. It's quite obvious that there is a gap between people that they constantly try to bridge. This attempt at bridging the gap comes in many forms of relationships, some good and some bad. Humans are communal beings at heart and basically spend their entire lives trying to unify with people. Reaching out to others is quite healthy and instinctual, however one should be careful that they do not reach out on the basis of attachment. Most people don't have a high sense of self worth, and as such are willing to basically delude themselves into thinking that "this is the best that they can get." This results in people hanging out with "friends" who don't really care about them, and this is done only to falsify a sense of acceptance.
Another big problem with false relationships is thinking of friends as property. For instance, saying something like: "I have a lot of friends." You don't actually "have" them, for you don't own them. Once one starts to think of friends on a non-attachmental basis, then they will enjoy them not as possession to be "consumed" but as true people who bring the most out of every moment with you. However when friends are not around one will not despair because nothing has been lost. Something must be possessed first in order to have lost it.
The very first person to look out for should be oneself before all others (I'll clarify this in later writings). In terms of relationships, the best way in which to do this is to freely love without thought of return. Doing so will result in those who are worth being friends with, responding in kind. Ironic isn't it that in being "selfish" will result in being unselfish. If someone does not respond to love in kind, then drop them and move on. You are better than that.
This was just a brief overview of the friendship relationship, I'll probably hit it again in more detail in the future.