In preparation for becoming confessors, we seminarians were taught of a sin called delectatio morosa, a lingering delight in past sins. I wish they had given us this description of it by John Donne. He is describing a moment in the process by which we achieve purity of heart:

When the heart is emptied of infidelity and of those habits of sin that filled it, when it is come to a discontinuance and a detestation of those sins, then we can better look into every corner and endeavor to keep it clean, clean in that measure that the God of pure eyes will vouchsafe to look upon it, and the light of his countenance will perfect the work. The diligence required on our part is a serious watchfulness and consideration of our particular actions, how small soever. In the Law, whatsoever was unclean to eat made a man unclean to touch it, when it was dead. Though the body of sin have so far received a deadly wound in thee, as that thou hast discontinued some habitual sin, some long time; yet if thou touch upon the memory of that dead sin, with delight, thou begettest a new child of sin. And as Isaiah speaks of a child, and of a sinner of an hundred years old (Is 65:20), so every sin into which we relapse is born an hundred years old; it hath all the age of that sin, which we had repented and discontinued before, upon it; it is born an Adam, in full strength the first minute; born a Giant, born a Devil, and possesses us in an instant. Every man may observe that a sin of relapse is sooner upon him than the same sin was at the first attempting him; at first, he had more bashfulness, more tenderness, more colluctation against the sin than upon a relapse. And therefore in this survey of sin, thy first care must be to take heed of returning too diligently to a remembrance of those delightful sins which are past; for that will endanger new. And in many cases it is safer to do (as God himself is said to do) to tie up our sins in a bundle and cast them into the sea (Mic 7:29), so for us to present our sins in general to God and to cast them into the bottomless sea of the infinite mercies of God, in the infinite merits of Christ Jesus, than by an over-diligent enumeration of sins of some kinds, or by too busy a contemplation of those circumstances which increased our sinful delights then when we committed those sins, to commit them over again, by a fresh delight in their memory. When thou hast truly repented them, and God hath forgotten them, do thou forget them too. (Sermon 3, 193-94)