1 John 5:18
 We know that everyone who has been born of God does not keep on sinning, but he who was born of God protects him, and the evil one does not touch him. (ESV)
This verse is challenging for us. John says that everyone born of God does not keep on sinning. Does he mean we will never sin again after we have been saved? We know that we all continue to fight with temptation. And John himself tells us in this Epistle that when we do sin we have an advocate in Jesus Christ:
1 John 2:1
 My little children, I am writing these things to you so that you may not sin. But if anyone does sin, we have an advocate with the Father, Jesus Christ the righteous. (ESV)
So, it is clear that we sometimes sin after we have been saved. The phrase, "keep on sinning," is important. It implies a lifestyle of sinning. In fact, there are those who have embraced certain lifestyles that are forbidden in Scripture and they brazenly claim, "This is who I am," while also claiming to know Christ. John would disagree with their claim. If they have embraced sinning as a lifestyle they have not truly come to know God.
This verse continues to bring encouragement to the believer by reminding us that Satan has limitations on how much he can bring against us. We are protected from the evil one. We can be tempted, but no more than what God permits. The story of Job helps us to understand the limitations that God places on the evil one.
Perhaps you are stressed by the fact that you have fought battles with sin and lost. Repent and be assured of forgiveness. God is in control. He will protect you from the evil one.