Nowhere does the Bible say that a Christian in this life will ever be completely perfect that is, free from all sin (1 John 1:8).
As long as we are on this earth, we will always struggle against temptation and sin. That is one reason Jesus taught His disciples to pray (in The Lord's Prayer), "Forgive us our sins ... And lead us not into temptation, but deliver us from the evil one" (Luke 11:4, Matthew 6:13).
Sometimes we sin by our actions; sometimes by our motives. Often we sin not because of what we do, but because of what we fail to do. For example, we fail to love or forgive others, or in other ways fail to do things we ought to do and that is sin.
However, there are three important truths we need to repeat over and over to ourselves. First, just because we sin does not mean we are no longer God's children. Our fellowship with God may be broken, but our relationship is not. Second, when we sin God stands ready to forgive us, and we need to turn to Him immediately.
"If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness" (1 John 1:9). Third, God wants to help us (through His Holy Spirit, who lives within every believer) to avoid sin in the future. "Live by the Spirit, and you will not gratify the desires of the sinful nature" (Galatians 5:16).
Thank God that you belong to Christ, and thank Him for His grace and forgiveness when you do sin and for strength to overcome future temptation. "My dear children, I write this to you so that you will not sin. But if anybody does sin, we have one who speaks to the Father in our defense Jesus Christ, the Righteous One" (1 John 2:1).