In principle, repentance implies an utter rejection of former sin. For example, a thief who repents will not only ask forgiveness for his former thefts but will also change his ways so that he does not steal any longer. Jesus said to the woman taken in adultery “go and sin no more” (John 8:11). So, in principle, if you truly repented of a particular sin then you would intend to never sin again.
However, none of us is perfect and so while we might intend to never sin again, we might be tempted into sin once more. Paul describes his own struggle:
“For I do not understand my own actions. For I do not do what I want, but I do the very thing I hate … it is no longer I who do it, but sin that dwells within me. For I know that nothing good dwells in me, that is, in my flesh. For I have the desire to do what is right, but not the ability to carry it out. For I do not do the good I want, but the evil I do not want is what I keep on doing. Now if I do what I do not want, it is no longer I who do it, but sin that dwells within me” (Romans 7:15-19).
Here Paul describes how he intends to do good, but there is something else inside him that tempts him to do evil. He says that sometimes he does things that he doesn’t want to do (i.e. he sins). This is the same for all of us.
When we repent we intend to never sin again, but we will still be tempted and sometimes sin. This failure does not necessarily demonstrate a lack of repentance but a failure of our will to do good.