Not even the stars are pure in the Lord's sight; how much less men whose whole life is one long temptation! Woe to us who commit fornication every time that we cherish lust. ‘My sword’, God says, ‘has drunk its fill in heaven;’ much more then upon the earth with its crop of thorns and thistles.
The “chosen vessel” through whom Christ spoke, consumed his body and brought it into subjection. Yet even he was hindered by carnal desire and had to do what he would not. As one suffering violence he cried: ‘O wretched man that I am! Who shall deliver me from the body of this death?’ (Rm 7:24) Is it likely then that you can pass without fall or wound, unless you watch over your heart with all diligence?
Saint Jerome
Letters, 125: 7
Cf http://www.newadvent.org/fathers/3001125.htm