Aelred of Rievaulx
Extracts from 'On Spiritual Friendship'
When I was still a boy in the schools and being liked by my companions was my chief delight, among the tendencies and frailties which are the particular temptations of that age, the pursuit of love and affection occupied my entire mind. There was in my eyes no greater pleasure, no keener joy, nothing more beneficial than loving and being loved. And as I see-sawed between various loves and friendships, my spirit was swept this way and that, and, knowing nothing of the law of true friendship, was often deceived by its simulacrum.
At last there came into my hands the book that Cicero wrote on friendship, which charmed me doubly by the weight of its argument and the grace of its style. And although I did not see myself as fit for that kind of friendship, I was none the less thankful to have met with a certain rule on which I might pattern my wandering loves and affections. When it pleased my good Lord to bring back the wanderer, to raise the fallen and to cleanse the leper by his healing touch, I abandoned worldly aspirations and entered the cloister. At once I devoted myself to the study of the Scriptures, the mere surface of which had been more than my bleary eyes could previously encompass, used as they were to the murk in which I lived. As my taste for Scripture grew, and the scraps of knowledge that the world had given me staled in comparison, I found myself thinking of what I had read in Cicero's book and was amazed to find that it no longer held the same savour for me. By then nothing that was not imbued with the sweetness of Jesus, nothing that not seasoned with the salt of Scripture could wholly capture my affection. 
So as I turned Cicero's arguments over in my mind, I was looking to see if they might perhaps be supported by the authority of Scripture. I had read a lot about friendship too in the writings of the Fathers, and, finding myself incapable of loving spiritually as I wished, I resolved to write about spiritual friendship and prescribe for myself rules of chaste and holy love. I have therefore divided this little work into three books: in the first setting out the nature of friendship, its origin and cause; in the second putting forward its merits and the benefits to be derived from it; in the last elucidating as best I can how, and between whom, it may be preserved unbroken to the end. If anyone should profit by reading it, let him give thanks to God and entreat Christ's mercy for my sins; and, if he should judge it to be unnecessary or useless, may he have compassion on my plight, which has forced me to interrupt my thoughts on this subject with practical concerns.
Since it is certain that many are deceived by the semblance of friendship, I wish you would explain what sort of friendships we should avoid, and which we should seek, foster and conserve.  Very well, I shall briefly list those we ought to shun. First, the adolescent friendship, the product of roving and undisciplined feelings, which stretch out their tentacles towards every passer-by; a friendship without reason, weight or measure, that takes no account of others' good or detriment. This kind of love affects one very powerfully for a time, it captivates and flatters. But affection devoid of rationality is an animal impulse leading to all that is unlawful; indeed it is incapable of distinguishing between what is and is not lawful. Although affection often precedes friendship, one should never give rein to it unless it is led by reason, tempered by integrity and ruled by righteousness. Therefore the friendship we referred to as adolescent - because in youth feelings predominate and relationships are always unstable, wavering in their loyalty and with an admixture of sensuality - such friendship is to be avoided at all costs by those who are drawn to the sweetness of spiritual friendship.