It happened to my brother who was going to Church before me, even though I am older than him.
He was strict about it too, and did a good job acting Christlike, attending a Church that upheld the holiness of Jesus, and it was a good Church with hypocrisy way down for I hung around them for I went to that Church, and they really loved acting like Jesus, and abstaining from the ways of the world.
But my brother let sin come in to his life to enjoy it, and one thing led to another with him enjoying more sin, and eventually left that Church, got married, and attended a Church with relaxed ways about them, which his wife's mom was a lesbian, so that Church probably saw nothing wrong with it.
He even got in to swinging with his wife, which I did not know about until my dad told me, but my brother would not tell me for he did not want me to be ashamed of him, for he always looked up to me, and really liked me.
But he ended up getting divorced, and living with my sister who goes to Church, so maybe he will get back to where he used to be if he is fed up with the world.
But how is the sin nature reactivated, if one starts to enjoy sin, for then it can led to other areas of sin.
But the sin nature does not go away, although we do not have to go by it, for Paul said in the flesh dwells no good thing, which he said when he does good, evil is present with him.
So the sin nature is always activated in the flesh, but we can go by the Spirit, and not the flesh, and with the mind serve Christ, and not let sin in action be activated.
For we are tempted, and if we are tempted then the sin nature is activated, but we do not have to make it an action.