We have to go to confession anytime we have committed mortal sin. There is no excuse for that at all.
About confessing to priests, let’s see what the Bible says or at least suggests.
“Therefore confess your sins to one another, and pray for one another, that you may be healed. The prayer of a righteous man has great power in its effects.” (James 5:16 RSV)
Also, After Christ Jesus death and resurrection, He came to His disciplines to tell them a secret I guess? :) Let’s see…
“On the evening of that day, the first day of the week, the doors being shut where the disciples were, for fear of the Jews, Jesus came and stood among them and said to them, “Peace be with you.” When he had said this, he showed them his hands and his side. Then the disciples were glad when they saw the Lord. Jesus said to them again, “Peace be with you. As the Father has sent me, even so I send you.” And when he had said this, he breathed on them, and said to them, “Receive the Holy Spirit. If you forgive the sins of any, they are forgiven; if you retain the sins of any, they are retained.”” (John 20:19-23 RSV)