Only God knows if someone has truly and sincerely repented of their sins and given their life to Jesus Christ as their Lord and Savior, but if they have, they now belong to Him forever, and their salvation is secure. The Bible says that nothing "will be able to separate us from the love of God that is in Christ Jesus our Lord" (Romans 8:39).
Remember: When we come to Christ, He comes to live within us by His Spirit -- and He will never depart from us. And when we come to Him, God adopts us into His family and we become His children -- and He'll never disown us or disinherit us. If He did reject us, it would mean our salvation depends on how good we are. But we can never be good enough, for God's standard is perfection. Our salvation depends solely on Christ, Who died to take away all our sins.
Does this mean it doesn't matter how we live? Absolutely not! If we live sinful lives, it may well mean that we haven't given ourselves to Christ after all, and we've even deceived ourselves into thinking we are saved when we really aren't. The Bible warns, "As the body without the spirit is dead, so faith without deeds is dead" (James 2:26).
Make sure of your commitment to Jesus Christ, both as your Savior and as your Lord. Then thank Him that you now belong to Him forever -- and ask Him to help you live a life that reflects His love and purity every day.