An insincere and evil friend is more to be feared than a wild beast; a wild beast may wound your body, but an evil friend will wound your mind. -Buddha

Etymologically the word ‘Metta’ means friendliness (mittassa sabhavo) but friendship encapsulates all the noble human feelings one can have for another.  Metta (loving kindness), Karuna (compassion), Muditha (altruistic joy) and Upeksha (equanimity) are known as the Four Noble patterns of behavior which form the anchor of Buddhist conduct. The spirit of love and friendship promulgated by these, cover a much wider spectrum than mere romantic  love.

William Shakespeare’s Sonnet #116 offers,

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Let me not to the marriage of true minds
Admit impediments. Love is not love
Which alters when it alteration finds,
Or bends with the remover to remove:
O, no! It is an ever-fixed mark
That looks on tempests and is never shaken

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Shakespeare describes an eternal, unconditional love which does not depend upon reciprocation, a love which can be a guiding and steadying force during storm or adversity. To Buddhists, friendliness, or loving kindness, is also like the North Star in that it guides and steadies one’s thoughts and actions throughout the voyage of life.

Associate yourself with men of good quality…for ’tis better to be alone than in bad company. -George Washington

The dharma abounds with examples of the essential guidance of good friends. The Buddha has described two types of friends, Kalyana Mitta (the good friend) and Papa Mitta (the evil friend). A famous stanza in the Dhammapada says, “Do not keep company with evil friends or those who are mean. Associate with the good and bold friends.” All parents should instill into the minds of their children the noble advice conveyed by this stanza. The Buddha advised us to lead a lonely life in case we cannot find a decent friend, but never to keep the company of a fool.

A Friend may well be reckoned the masterpiece of Nature. -Ralph Waldo Emerson

Mahamangala Sutra enumerates 38 of life’s greatest blessings to guide one in life’s journey.  First among them is a blessing to avoid the company of fools.
Friendship is a force that has no parallel; there is no other single power that can generate good qualities in a person as quality friendship because, after a certain age, we stop emulating our parents and start imitating our friends.

In Samyutta Nikaya, Ananda remarked that “half of the dispensation is based on friendship, companionship and association with the good.”  To which the Buddha replied, “Not half, but man’s entire life is established on friendship, companionship and association with the good.”

In the Sigalovada Sutra, the Buddha first explains the characteristics of an evil friend.  A foe in the guise of a friend will appropriate a friend’s possessions, render mere lip service, flatter, will give little with the idea of taking much, will associate for his own advantage, tries to gain favor by empty words and when the opportunity arises for action, he will give an excuse and express his inability to render any service. An evil friend also praises and approves his friends bad deeds while the good deeds go unnoticed and upraised. He praises the friend in his presence and rebukes him in his absence.

Someone who points out your mistakes, declare them as weaknesses and condemns them, think of such a person as one showing you a treasure. -Buddha

An insincere and evil friend is more to be feared than a wild beast; a wild beast may wound your body, but an evil friend will wound your mind. -Buddha

The Buddha then explained how a foe in the guise of a friend (mitta patirupaka) brings about ruin in four ways:

He is a companion in indulging in intoxicants which gives rise to infatuation and heedlessness.

He is a ready companion to frequent the streets at ungodly hours.

He is a companion to attend theatrical shows and
He is a companion in gambling which causes one’s downfall.

“The best mirror is an old friend.” -George Herbert
Next, the Buddha enumerates the four types of friends who should be cherished as a mother tends her only son.
He who is a helpmate,
He who is steadfast and unchanging in happiness or sorrow,
He who gives good counsel and
He who sympathizes

According to Nettippakarana there are seven qualities of a friend. He should be:

pleasant and lovable,
respectful,
worthy of emulation,
a useful conversationalist,
tolerant of words,
engages in profound talk and
never exhorts groundlessly or urges you to take unreasonable actions.

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We have a tendency to shun good advice and show resentment when our faults are pointed out.  In the Dhammapada, Buddha offers this excellent advice, “Someone who points out your mistakes, declares them as weaknesses and condemns them, think of such a person as one showing you a treasure.” This shows that a true friend should not remain mute to avoid conflict, but rather tell hard truths and offer constructive criticism.  Friendship must have some edge to it, or else it is not one.  In friendship, one blade sharpens the other.

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“The only reward of virtue is virtue; the only way to have a friend is to be one.”  – Ralph Waldo Emerson
The Buddha has explained how to win and keep friends. By being generous one can surely win friends and also by being courteous and benevolent. Rejoice in your friend’s achievements, praise any commendable acts and strong points. A friend is one who incessantly pays us the compliment of expecting from us all the virtues, and who can appreciate them in us. Similarly, Henry David Thoreau wrote, “The friend asks no return but that his friend will religiously accept and wear and not disgrace his apotheosis of him. They cherish each other’s hopes. They are kind to each other’s dreams.”
But the Buddha says that if you talk only of your friend’s good qualities, then you are trying to deceive him. In dealing with friends, one’s word should be as clean as one’s actions.
In the Jataka Pali, Buddha has given invaluable advice not only how to keep the friendship, but also how to make the bonds stronger. One should not visit friends too often or overstay one’s welcome.
  This can change a friend to a foe. Also, if your friend loses something, then you may be under a cloud. Visiting a friend too often invariably leads to gossip, which will involve you in a vortex of trouble.

Buddha says that, it is equally bad not to visit your friends at all.  Buddha has pointed out that a friendship deteriorates by asking favors, especially at wrong times. If at all you ask a favor, it should not be unreasonable or of a demanding nature. Asking favors far too often makes you a pest more than a friend.
Buddha has explained that if someone wants to bring about his own ruin or downfall, he could associate with Papa mitta or evil friends, including gamblers, libertines, cheats, swindlers or violent thugs.

Friendship Is the Only Cement That Will Ever Hold the World Together. -Woodrow Wilson

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“A friend is one whose association leads to spiritual profitability, protects you from evil that may befall you and is inclined towards your welfare.” -Traditional Buddhist Saying
Buddhism provides the basic ingredients to foster a healthy friendship, minimize friction and displeasure, promote good will, and companionship and ultimately bring about one’s welfare here, and spiritual progress leading to the realization of the supreme bliss of Nirvana.  Buddha’s words on choosing friends, winning them and keeping them expounded in the 6th Century B.C.E., seem to surpass all books of the twentieth century on the subject.  Clearly, the Buddhist concept of friendship should forever remain a useful and vibrant force to help with the appreciation and fulfillment of life.