We are more or less guilty depending on 1) how serious the sin is in itself; 2) our knowledge that we are sinning; 3) our *free *consent to sin anyway. If grave matter, full knowledge or full consent is lacking, the sin is not mortal.
Factors like ignorance, addiction, mental illness, and coercion can make our acts less free and deliberate, and therefore less serious, subjectively speaking, although they may be serious in themselves. Note, however, just because one of those factors is in play, doesn’t *necessarily *mean the sin is not mortal. And just because it’s not mortal, doesn’t mean it’s no big deal. A good confessor can help you discern in a given case.