Romans 8:1-4 (ESV)
8:1 There is therefore now no condemnation for those who are in Christ Jesus. 2 For the law of the Spirit of life has set you free in Christ Jesus from the law of sin and death. 3 For God has done what the law, weakened by the flesh, could not do. By sending his own Son in the likeness of sinful flesh and for sin, he condemned sin in the flesh, 4 in order that the righteous requirement of the law might be fulfilled in us, who walk not according to the flesh but according to the Spirit.
*When you are in Christ, there is no need to feel bad about a mistake. The idea is to ask God to help us change our thought process, and to learn from the situation or choice. However, do not fall into condemnation about it, or allow others to hang it over your head. If we are truly in Christ, we know that He has already paved the way for us to be free from sin. Even more so, our love for God should make us want to remove ourselves from sinful situations that can lead to habitual behavior. Find peace in letting go in order to gain more.