[Serious] For former Christians only, why did you leave your faith?

[BrianSoddingBoru4]

The act of masturbation is a mortal sin, full stop. The are no conditions or intentions which make it venial. Which is another good reason to leave the Church.

Also, there is no requirement to confess venial sins (it is, however, strongly encouraged).

Boru

From the Horse's mouth (no pun intended):

2352 By masturbation is to be understood the deliberate stimulation of the genital organs in order to derive sexual pleasure. "Both the Magisterium of the Church, in the course of a constant tradition, and the moral sense of the faithful have been in no doubt and have firmly maintained that masturbation is an intrinsically and gravely disordered action." "The deliberate use of the sexual faculty, for whatever reason, outside of marriage is essentially contrary to its purpose." For here sexual pleasure is sought outside of "the sexual relationship which is demanded by the moral order and in which the total meaning of mutual self-giving and human procreation in the context of true love is achieved."
To form an equitable judgment about the subjects' moral responsibility and to guide pastoral action, one must take into account the affective immaturity, force of acquired habit, conditions of anxiety or other psychological or social factors that lessen, if not even reduce to a minimum, moral culpability.

None of which changes it from a mortal to a venial sin. ‘Moral culpability’ is not the same as sin.

Boru