Romans 14:23 - "whatever is not from faith is sin."
All sin is faithlessness. The sin that condemns is blaspheming the Holy Spirit, calling Him evil when He points us to the Savior. This is a rejection of faith in the Lord Jesus. But every other sin we commit, is a lack of faith, too. In fact, any thing we do can be sin if we do it without faith. Faith does good works; disbelief brings sin. The ultimate sin that separates us from God is not believing Him. When you sin, get back to the heart of the matter. Confess your behavior, but then confess the lack of faith causing it. Ask for God to change your heart to be loyal and loving of Him again.