He admits going into her room while she slept and touching her crotch on six to 10 separate occasions but the victim does not remember any more than two.
The victim's mother found him asleep on the floor beside the girl's bed a number of times.
In a conversation with an acquaintance, De Vries mentioned Old Testament bible verses about how if a woman has sex with a man in a city but does not cry out for help, then it is deemed consensual.
When the teenager revealed the abuse to her pastor, De Vries wrote her a letter saying he was sorry she had to relive the pain of past sin, and offering advice that she should seek counsel from "godly men in the church" and men who knew about the complaints process.
De Vries gave evidence this week, saying he did not realise it at the time, but looking back realised he was using the victim as an object for his sexual gratification.
He would regularly kneel beside her bed, hold her hand, run his fingers through her hair, kiss her face, and touch her breasts.
Crown prosecutor Harry Mallalieu said De Vries was "obsessed" with the girl.
The victim would try to sew her pyjama buttons together to stop him undressing her.
De Vries will be sentenced on October 3.
