"Jealousy never arises where love is built up on true virtue, and therefore it is a sure sign of an earthly, sensual love, in which mistrust and inconstancy is soon infused. It is a sorry kind of friendship which seeks to strengthen itself by jealously; for though jealousy may be a sign of strong, hot [...]
"Of course, we should love him notwithstanding his faults, but without loving those faults; true friendship implies an interchange of what is good, not what is evil." Source: St. Francis de Sales, Introduction to the Devout Life, Random House, Inc., 2002.
"Friendship demands very close correspondence between those who love one another, otherwise it can never take root or continue." Source: St. Francis de Sales, Introduction to the Devout Life, Random House, Inc., 2002.
"And St. Thomas, in common with other philosophers, acknowledges that friendship is a virtue, and he certainly means individual friendships, because he says that we cannot bestow perfect friendship on many persons." Source: St. Francis de Sales, Introduction to the Devout Life, Random House, Inc., 2002.