What deadly sin are you referring to here?
According to Christian tradition the seven deadly sins are: envy, gluttony, greed or avarice, lust, pride, sloth, and wrath.
Please note, the early church classified the seven deadly sins as cardinal sins or capital vices and taught that they could not be forgiven. However, according to the Bible these 7 deadly sins are completely and totally forgivable by God, but this doesn’t give free license to commit these sins. Biblically, the only sin that cannot be forgiven is complete rejection of God’s grace which is outright rebellion against God, also known as blasphemy against the Holy Spirit.