Grace, salvation, and the last things · Question 5
If I commit one grave sin, is the road to salvation over forever?

The question: “If I think I've committed a mortal sin, does God give up on me right away?”
The Church's answer: A mortal sin is a sin that destroys love, chosen in full freedom and with full knowledge of a grave matter. It is a serious choice that costs us sanctifying grace, so it can't be made light with “once won't hurt.” At the same time, the fact that an act looks serious does not put us in a position to judge the whole of another person's knowledge, freedom, and state of soul.
God waits for the sinner to come back and never shuts the road of repentance. For a believer who has committed a mortal sin after baptism, the sacrament of confession is the ordinary road to reconciliation. Admit the wrong honestly, begin whatever repair of the harm is possible, and ask a priest for help in receiving the sacrament. Avoid both the despair that says “it's over anyway, so it doesn't matter if I get worse” and the calculation that says “I can confess later, so I can do it now.”
If they press further: “What if I keep getting confused and frightened about whether it was mortal?” — don't sit alone passing judgment on grave matter, full knowledge, and full consent from an internet checklist. Get calm help from one trustworthy confessor, and if you have a compulsion to check the same doubt endlessly, get professional counseling alongside it. What you need is not someone who feeds the fear but a guide who teaches God's mercy and responsibility together.
In one sentence: “A mortal sin is a serious choice that destroys love, but it doesn't mean God gives up on someone who repents. Don't hide and don't despair — come back through the sacrament of reconciliation and responsible repair.”