“The person who has many friends, will be forced by necessity to create some imaginary enemies inside his mind.”

The Society of Mind (1987)

There is no known basis to attribute this saying to Napoleon. It is found (unattributed) in a Usenet post from July 1999 https://groups.google.com/forum/message/raw?msg=soc.penpals/QIUrpkacWyE/FbCj7pij5WwJ.
Misattributed

As quoted in "Considerations By the Way" in Conduct of Life by Ralph Waldo Emerson
Variant translation: Believe me, a thousand friends suffice thee not; In a single enemy thou hast more than enough

1950s, Loving Your Enemies (Christmas 1957)
Context: A third reason why we should love our enemies is that love is the only force capable of transforming an enemy into a friend. We never get rid of an enemy by meeting hate with hate; we get rid of an enemy by getting rid of enmity. By its very nature, love creates and builds up. Love transforms with redemptive power.

Quoted by George Bernard Shaw in a letter to Ellen Terry, 25 September 1896.
Context: On George Bernard Shaw An excellent man: he has no enemies, and none of his friends like him.

the desire for pleasure. The monks and the sannyasis of the world have tried to go beyond it, have forced themselves to worship an ideal, an image, a symbol. But desire is always there like a flame, burning. And to find out, to probe into the nature of desire, the complexity of desire, its activities, its demands, its fulfilments — ever more and more desire for power, position, prestige, status, the desire for the unnameable, that which is beyond all our daily life — has made man do all kinds of ugly and brutal things. Desire is the outcome of sensation the outcome with all the images that thought has built. And this desire not only breeds discontent but a sense of hopelessness. Never suppress it, never discipline it but probe into the nature of it — what is the origin, the purpose, the intricacies of it? To delve deep into it is not another desire, for it has no motive; it is like understanding the beauty of a flower, to sit down beside it and look at it. And as you look it begins to reveal itself as it actually is — the extraordinarily delicate colour, the perfume, the petals, the stem and the earth out of which it has grown. So look at this desire and its nature without thought which is always shaping sensations, pleasure and pain, reward and punishment. Then one understands, not verbally, nor intellectually, the whole causation of desire, the root of desire. The very perception of it, the subtle perception of it, that in itself is intelligence. And that intelligence will always act sanely and rationally in dealing with desire.
Krishnamurti to Himself (1987) http://www.jkrishnamurti.com/krishnamurti-teachings/view-text.php?tid=16&chid=609 - ISBN 0-06-250649-8 1993 edition; J.Krishnamurti Online. Serial No. 60039
1980s

Source: Epistulae Morales ad Lucilium (Moral Letters to Lucilius), Letter II: On discursiveness in reading, Line 2.