My current, imperfect, understanding about the sinful nature and the new nature in Christ is like this: imagine three plastic water containers each holding let’s say 50 gallons of water, A, B, and C.
A is the sinful nature, B is the new nature, the new life in Christ, and C is your active soul that you’re actually living by.
You can hook up either to A sinful nature; or B the life in Christ.
Most of us believers have this fine mix between the two, so we have sinful motivations and then also pure loving and godly motivations. You have a mixed stream between the two water sources and we go to one or the other then we get those results.
The unbeliever only has one source but the motivations and the actions can be so bad they modify them to make them look right, but they are really not from the same source as from the Spirit of God.