Frequent not the company of immodest persons, especially if they be also impudent, as is generally the case; ...these corrupted souls and infected hearts scarcely speak to any, either of the same or a different sex, without causing them to fall in some degree from purity; they have poison in their eyes and in their breath, like basilisks. On the contrary, keep company with the chaste and virtuous; often meditate upon and read holy things; for the word of God is chaste, and makes those also chaste that delight in it.
Saint Francis de Sales
In Tibet there is no marriage, and there is no jealousy, yet we know that marriage is a much higher state. The Tibetans have not known the wonderful enjoyment, the blessing of chastity, the happiness of having a chaste, virtuous wife, or a chaste, virtuous husband. These people cannot feel that. And similarly they do not feel the intense jealousy of the chaste wife or husband, or the misery caused by unfaithfulness on either side, with all the heart-burnings and sorrows which believers in chastity experience. On one side, the latter gain happiness, but on the other, they suffer misery too.
Today all good things are made lawful for you. And the food of those given the Scripture is lawful for you, and your food is lawful for them. So are chaste believing women, and chaste women from the people who were given the Scripture before you, provided you give them their dowries, and take them in marriage, not in adultery, nor as mistresses. But whoever rejects faith, his work will be in vain, and in the Hereafter he will be among the losers.
[Y]ou are not ashamed of your sin [in committing adultery] because so many men commit it. Man's wickedness is now such that men are more ashamed of chastity than of lechery. Murderers, thieves, perjurers, false witnesses, plunderers and fraudsters are detested and hated by people generally, but whoever will sleep with his servant girl in brazen lechery is liked and admired for it, and people make light of the damage to his soul. And if any man has the nerve to say that he is chaste and faithful to his wife and this gets known, he is ashamed to mix with other men, whose behaviour is not like his, for they will mock him and despise him and say he's not a real man; for man's wickedness is now of such proportions that no one is considered a man unless he is overcome by lechery, while one who overcomes lechery and stays chaste is considered unmanly.
Augustine of Hippo