OSAS doctrine claims - Nothing you do can affect the outcome of your salvation since you are saved by Grace.
According to your examples above , one can become unsaved.
You cannot state he was never saved to begin with cause your hypothesis shows clearly he was at one time believing and loving Christ , then he stoped producing fruits which is discontinuing his love for Christ.
If fruits stop, Love stops, if love stops, Faith stops.
Faith = Love= fruits = Salvation and judgement.
Faith
Love
Fruits
Zeke