You have sent a letter to me through the hand of a "friend" of yours, as you call him. And in your very next sentence you warn me not to discuss with him all the matters that concern you, saying that even you yourself are not accustomed to do this; in other words, you have in the same letter affirmed and denied that he is your friend. Now is you used this word of ours in the popular sense, and called him "friend" in the same way in which we speak of all candidates for election as "honourble gentlemen," and as we greet all men whom we meet casually, if their names slip us for the moment, with the salutation "my dear sir,"-so be it. But if you consider any ma a friend whom you do not trust as you trust yourself, you are mightily mistaken and you d not sufficiently understand what true friendship means...
You desire to know whether Epicurus is right when, in one of his letters, he rebukes those who hold that the wise man is self-sufficient and for that reason does not stand in need of friendships. This is the objection raised by Epicurus against Stilbo and those who believe that the Supreme Good is a soul which is insensible to feeling. We are bound to meet with a double meaning if we try to express the Greek term "lack of feeling" summarily, in a single word, rendering it by the Latin word impatientia...
When I urge you so strongly to your studies, it is my own interest which I am consulting; I want your friendship, and it cannot fall to my lot unless you proceed, as you have begun, with the task of developing yourself. For now, although you love me, you are not yet my friend. "But," you reply, "are these words of different meaning?" Nay, more, they are totally unlike in meaning. A friend loves you, of course; but one who loves you is not in every case your friend. Friendship, accordingly, is always helpful, but love sometimes even does harm, Try to perfect yourself, if for no other reason, in order that you may learn how to love....
Click on the links to read the entire writing translated by Richard M. Gummere.