Since repentance doesn't necessarily mean that we won't commit the same mistakes after becoming a Christian, how does one know when their slip-ups are due to weakness and struggling with old sins or habits? If they really are trying to overcome those sins and then repeat mistakes, how do they really know they haven't repented and returned from sin? How does one know the difference? I ask because this article, Is masturbating wrong for women? addresses something I had struggled with for a while. I repented of this before my baptism and was determined to not repeat it because I wanted to give it up for good. There were times when temptation arose afterward and I fought against it each time. Then one time came where I slipped again because I didn't control my thoughts as well as I should have. I was determined to never do it again and yet it happened. Since then I've been even more determined to fight against this sin and not repeat it. If slipping doesn't negate the fact that one repented when they became a Christian, how do we know when our slip-ups are due to weakness or when they are due to a lack of true repentance? How do you differentiate between a repeat mistake due to a weak area and one that is due to lack of repentance?
Repentance translates a Greek military word for doing an about-face. You are changing directions to go back. In a moral sense, it means you are turning around to go back to God.
A person who doesn't repent doesn't try to change. For example, Esau badly wanted a blessing but he did nothing to change his behavior (Genesis 27:30-41). In fact, just a few verses later we find him marrying a third wife because his parents didn't like his first two wives (Genesis 38:8-9). "See to it that no one comes short of the grace of God; that no root of bitterness springing up causes trouble, and by it many be defiled; that there be no immoral or godless person like Esau, who sold his own birthright for a single meal. For you know that even afterwards, when he desired to inherit the blessing, he was rejected, for he found no place for repentance, though he sought for it with tears" (Hebrews 12:15-17).
A weak person might give in to sin, but he eventually realizes he is off-course and becomes determined to change. "For a righteous man falls seven times, and rises again, But the wicked stumble in time of calamity" (Proverbs 24:16).
You struggle with lust, but the point is that you are struggling and have not given up.