Friendship was a topic of interest to the ancient philosophers. Plato talked about it, Aristotle, and it was Cicero's De Amicitia that set the pace for Medieval considerations of it. Friendship is not a topic of direct consideration in Scripture, although it makes a pronounced appearance in the Gospel of John. The thing with the Bible is that it's interested in the relationship between God and man, and not man and man per se, but I wouldn't stretch the point too far. If there is one thing that unites the Bible as a whole (and there is!) it is that it's about the relationship with God. John tells us that Christ is our friend, but the favoured metaphor of the Old Testament (other than 'Lord', of course) is lover. God is our lover - Israel's, the prophet's, etc. This definitely carries over into the New Testament. By why the shift in John?
I no longer call you servants, because a servant does not know his master's business. Instead, I have called you friends, for everything that I learned from my Father I have made known to you.
This is often abbreviated to I no longer call you servants, but friends. But this is to remove the meaning of the shift, thus turning it into a hallmark platitude.
John mentions 'friend' seven times, Matthew four, Mark not at all, while Luke uses the word sixteen times. The most significant use of the last lies with the phrase "friend of tax collectors," etc. That phrase just has the ring of the core First Century kerygma to it (spoken rather than writing tradition that predates the latter).
With this pedigree, I do not think that we can say that friendship is not a Christian idea. But neither can we say that there is no significant difference between the pagan philosophical notion and the Christian. We just don't find a non-theological treatment of it at the heart of our notion. This means that friendship for us will also be 'in God,' if not simply 'with God.' An implication of this is the tendency to ignore what friendship is exactly, since the the difference between 'in God' and 'with God' is vast. In the former case we find the mutuality of need and benefit but by no means in the latter. This is the difference between eros and agape. Eros is a need-based love, while agape is the love of which greatness alone is capable. (See Benedict's first encyclical, or Anders Nygren's seminal work on this.) The difference between these two kinds of love is vast, and when you realize the difference signified by agape on God's side you realize that friendship with God is vastly different from friendship with another human person.
Now prescinding from this difference, I have found that there is an abuse that can creep into the Christian notion of friendship because of the theological horizon in which it is set. People sometimes think that they are capable of agape. And so they understand the requirement of putting God first as an indictment of mutuality. They still act as benefactors to others, but attempt to remove from themselves any emotive 'need' of the other, believing themselves capable of the type of love of which God alone is capable. Oftentimes works like the Imitation of Christ and the works of Theresa of Avila and John of the Cross are cited as suggesting as much. There are two errors here: (1) With respect to those works it has to be recognized that these were written for religious, not lay people; religious, moreover who do not in any way conform to the contemporary notion of the contemplative or even 'mixed' life. (2) Religious are not capable of agape either. This means that the duty of religious to become detached is not the duty 'to love but not be loved.' The Medieval Cistercians (especially) who considered this matter did not define friendship in such a manner to suggest that eros be changed into agape. They were theologically astute enough to know why this could not be.
The most important implication of all of this is that it is okay, even good, to draw strength from another human person.This might, for some of the reason alluded to above, be thought to deviated from the Christian tradition, but, likewise for the reasons cited above, it does not. It is easy to misinfer what these important spiritual works imply for the life of the lay person.
The idea that we ought to shift from eros to agape (like the idea that we can be perfect as our Heavenly Father is perfect) is not equivalent to the truth that we ought to move from selfishness to selflessness. Even in the great virtue of selflessness do we find the gift of grace. In other words, it is a result of God's agape that you even have a will of benefaction. This signifies that our eros is enduring - for we were in need of something and we received it from God. The error here comes out in the form of the radical vices of egoism and insensitivity, precisely the things the claim to agape was was meant to erase. A shakey foundation cannot support a real edifice. The type of egoism I mean is the belief that one can help others but does not lie in need of them. It is an estimation of your greatness relative to others. A bad road to begin on, indeed. It ends poorly because it begins in error, an error fuelled by original hubris, an act aimed at satisfy hubris with more of the same.
Part of the mistake people make with respect to this is to think that since God gives without receiving, and I should be like God, I should give without receiving. The difference is, God can give without receiving while you cannot. Realizing all of this should promote a realistic view of self and ultimately a realistic view of the other. Saintly people should be more capable of friendship than non-saintly people. Supposed saintly seem very often to be less capable of friendship. I am suggesting that one revisit their original assumption about that person's holiness. There is much more that can and should be said here. But I think I'll leave it with that: saints are better friends than non-saints.
But I will not let creep in the Jansenistic sense of it's-for-your-own-good idea of friendship that often appears at this point in the meditation. I am being a friend, such a person would suppose, by condemning you decisively and not walking with you in your poverty. Instead my sole function as your friend it to tell you about your poverty then move on.