I remember nuns saying that every time someone sins, he puts another nail into Christ. Is it because Jesus suffers every time we sin?
The Catechism of the Catholic Church contains these words:
Since our sins made the Lord Christ suffer the torment of the cross, those who plunge themselves into disorders and crimes crucify the Son of God anew in their hearts (for he is in them) and hold him up to contempt. And it can be seen that our crime in this case is greater in us than in the Jews. As for them, according to the witness of the apostle, “None of the rulers of this age understood this; for if they had, they would not have crucified the Lord of glory." We, however, profess to know him. And when we deny him by our deeds, we in some way seem to lay violent hands on him. Nor did demons crucify him; it is you who have crucified him and crucify him still, when you delight in your vices and sins. (CCC 598, quoting St. Francis of Assisi,Admonitio 5.3)