Do not allow thyself to violate the Divine commandment for the sake of human friendship.
Venerable Anthony the Great
I roamed about in such blindness, that I was ashamed not to have as much shamelessness as my comrades had; from day to day I grew more wanton, so as not get a reputation with them as a dishonorable man by being honorable…O my God! Thou didst see with what pleasure I walked along the streets of Babylon, and how I enjoyed wallowing in filth, as if it were the most precious balsam. The unseen enemy trampled me under his feet and led me according to his will, for I, the poor one, went after him everywhere with joy. From what did such blindness arise? O inimical friendship! Thou dost corrupt the hearts of young people so much, that not for their own gain, nor in order to do evil to another, but without purpose, as a joke only, they do evil. It would happen that they would only say, "Come with us and let us do this or that" and I would be ashamed not to indulge in every wanton impulse.
Blessed Augustine
Do not make acquaintances with a wicked man: friendship with the wicked is friendship with the devil.
Venerable Anthony the Great
A forward man soweth strife: and a whisperer separateth chief friends.
Proverbs 16:2.8
"A faithful friend is beyond price" (Ecclesiasticus 6:15), since he regards his friend's misfortunes as his own and suffers with him sharing his trials until death. A true friend is one who in times of trial calmly and imperturbably suffers with his neighbor the ensuing afflictions, privations and disasters as if they were his own. Do not lightly discard spiritual love: for men there is no other road to salvation. Because today an assault of the devil has aroused some hatred in you, do not judge as base and wicked a brother whom yesterday you regarded as spiritual and virtuous; but with longsuffering love dwell on the goodness you perceived yesterday and expel today's hatred from your soul.
Saint Maximus the Confessor
from Four
Centuries on Love, quoted from Volume Two of the Philocalia
[English language edition].
A faithful friend is a strong defense: and he that hath found such an one hath found a treasure. Nothing doth countervail a faithful friend; and his excellency is invaluable. A faithful friend is the medicine of life. (Ecclesiasticus 6:1416)
Indeed, the services of a faithful friend are invaluable. If thou fall into calamity or woe a faithful friend will try to rescue thee from calamity; a faithful friend will not spare his tranquility, health and property in order to alleviate thy situation; a faithful friend, if not by deed, then by means of good counsel will help thee, for, after all, good counsel in a timely manner is more precious than gold; a faithful friend by his concern alone will alleviate three woes. Woe is heavy when there is no one to express it to; but it is fully alleviated if there is a being near to us before whom we can pour out our heart and in whose sympathy we do not doubt.
Bishop Bessarion of Kostroma
Greater love hath no man than this, that a man lay down his life for his friends.
John 15:13