William Shakespeare gave some sound money advice in one of his works, Hamlet. In the book, a father, Polonius, advices his son on how to conduct himself in the world. He speaks about life in general, but we are particularly interested in the friendship and borrowing part:

Neither a borrower nor a lender be,
For loan oft loses both itself and friend,
And borrowing dulls the edge of husbandry.

In simpler words:

1. Don’t loan or borrow money
2. When you loan someone money and they don’t pay you back, you stand a chance of losing the money and your friend. Hitching debts on personal relationships will be the beginning of resentment and default.
3. Husbandry here refers to productivity. When you become dependent on borrowing money, you lose the motivation to work for money, so you keep on borrowing and borrowing some more.

You might also find the rest of the advice given by Polonius to his son useful.

Be friendly, but not common; don't dull your palm by effusively shaking hands with every chance newcomer. Avoid quarrels if you can, but if they are forced on you, give a good account of yourself. Hear every man's censure (opinion), but express your own ideas to few. Dress well, but not ostentatiously.