Q. 1183. What is presumption?
A. Presumption is a rash expectation of salvation without making proper use of the necessary means to obtain it.
Q. 1184. How may we be guilty of presumption?
A. We may be guilty of presumption:
1. By putting off confession when in a state of mortal sin;
2. By delaying the amendment of our lives and repentance for past sins;
3. By being indifferent about the number of times we yield to any temptation after we have once yielded and broken our resolution to resist it;
4. By thinking we can avoid sin without avoiding its near occasion;
5. By relying too much on ourselves and neglecting to follow the advice of our confessor in regard to the sins we confess.
In the situation you describe, the sin to be the most worried about is the sin of presumption. The sin of presumption starts out with committing small sins presuming that God will forgive them. But over time our conscience will become dulled to sin and we will be led to presume that God will forgive our mortal sins. However, at that point, because of our presumption, we will be missing the necessary condition for the forgiveness of mortal sins: sorrow for our sin.