How can one discern whether or not he is in mortal sin when a sin becomes habitual (e.g. masturbation). Priests often have varying answers that confuse laity.

If a sin becomes habitual one ordinarily still confesses it and doesn’t receive Holy Communion until one has received absolution. You may think that this is some more bluntness. My concern is not with being blunt as with being clear because many priests have made the whole matter cloudy in their desire to show compassion.

Certainly, there are factors that can mitigate the moral seriousness of the act (e.g., not being entirely awake or simply the force of habit). But as with all habitual sins, one must be careful to not use the notion of habit as an excuse to continue sinning. One is obliged to avoid the temptation that brings on the sin. It is possible to overcome habitual sin with the grace that God gives us. Having the same confessor who gets to know one can be a great help in discerning the morality of one's habit of sin.