I wonder if the OP's GF's mother knows that God has instructed the OP to have sex with her daughter and that while he and his GF are already married now, it will only last until December. I wonder if the GF knows?
Personally, I don't think the OP is religious, I think he's mentally ill. And horny. And instead of finding like-minded 19-year-old girls for some good clean fun, he's decided to dominate (in more ways than one by golly!) the entire life of a minor girl, and use his religious delusions to support what he's doing. This is criminal (even if he's not having sex with her) and I wish there was some way we could stop him. Now.