You are not a 'sinner saved by Grace'.
You were a sinner.
When you believed on and received Christ Jesus as your Saviour and Lord:
→ the old man died
→ you became a New Creature
To continue to identify as a sinner when you are now a New Creature In Christ Jesus is Spiritual Adultery.
Faithfulness to Christ Jesus requires that we totally reject your old identity and fully accept your New Identity.
Our old identity was defined by our Sin Nature.
Our New Identity is defined by our New Spirit.
The criticality of being faithful to Christ Jesus cannot be overstated.
When a believer sees themself as still a sinner
→ they keep the door open for sin
→ they deny the efficacy of Christ's finished work
Obviously, such an 'open marriage' to Christ is impure. Just as in the marriage between a man and a woman, unfaithfulness undermines their love and unity which translates into weakness and ultimate failure.
Our faithfulness to Christ Jesus is defined by our knowledge and acceptance of His Word as the Truth about our New Identity.
Believers who are ignorant of the Word cannot help but be unfaithful to it. Believers who resist the Word are intentionally unfaithful to it.
Since Jesus is the Incarnate Word, ignorance of and resistance to the Word results in Spiritual Adultery.
A minister counselling a couple who intend to marry would warn them to resist any future opportunities to commit adultery.
Likewise, a minister counselling a new believer should warn the believer to resist Satan's attempts to get them doubt who they are In Christ Jesus and, in so doing, commit Spiritual Adultery.
Because of a lack of teaching the Truth, and in some cases teaching error, believers are not given the proper understanding and expectation of their New Identity In Christ Jesus. In such cases, the believer cannot help but be spiritually unfaithful.
But even those who are taught the death of the Old Man and their New Birth identity can fail to walk in it. This is because they have not fully committed themselves to what they were taught.
In we hear Jesus telling those believers who have failed to walk in their New Identity to go back to their first love and do their first works.
Our first love is the realization of forgiveness of sins and our acceptance by Christ Jesus. Our first works are our faith in the power of His blood to cleanse and the power of His Holy Spirit to sustain us and empower us to live as Sons Of God.
So, whether you are a new believer or one who has followed Christ for years, the command from our Lord is to lock in on our relationship to Him in faith that His Word will manifest by His Holy Spirit in us.