I love Christ, but I struggle constantly with sin in my life. Should I doubt my salvation?
Not necessarily. Even the apostle Paul experienced perpetual struggle with sin throughout his life (Romans 7:7-25).
All of us struggle continually with sinful thoughts, sinful attitudes, sinful habits, and sinful desires. It is those who don't struggle—those who deliberately and eagerly revel in their sin—who need to have their sense of security shaken. So don't give up in defeat if you find yourself struggling with sin or even if you fall into it. Stay in the battle.
Fight sin by considering deeply what makes you more vulnerable to it, and then establish godly practices in its place. You may find you need to have accountability with a godly person you trust, or spend more time in prayer, or stay away from things that tempt you.
Do whatever it takes to discipline yourself and stop any pattern of sin before it gets started again. That is the key to staying away from sin—the constant, daily practice of thinking on the right things and not making provision for the flesh and its desires (Romans 13:14).