Two's a company, but three's a crowd. An Apple a day keeps the doctor away. If you can't beat them, join them. Don't count your chickens before they're hatched. Absence makes the heart grow fonder.
Blood is thicker than water.
A friend in need is a friend indeed. A friend who shares is a friend who cares. Love is blind. Actions speak louder than words. A bird in the hand is worth two in the bush.