And you also were included in Christ when you heard the message of truth, the gospel of your salvation. When you believed, you were marked in him with a seal, the promised Holy Spirit, who is a deposit guaranteeing our inheritance until the redemption of those who are God’s possession—to the praise of his glory. (Eph.1:13-14)
That's the promise of the gospel, there can be times when your not in fellowship, but the promise is that the Holy Spirit will be with you forever:
If you love Me, you will keep My commandments. And I will ask the Father, and He will give you another Advocate to be with you forever— the Spirit of truth. The world cannot receive Him, because it neither sees Him nor knows Him. But you do know Him, for He abides with you and will be in you. (John 14:15-17)
Grace and peace,
Mark