I got better results when I started a new save with a spellcaster. She had a few skills but no spells or perks to give her an advantage but Greg seemed to take a real liking to her and was always in a playful mood when she visited. She is a romance sim but her flirty mood always got overridden by her being scared around him so she didn't have that on her side either. But somehow romance blossomed and now she is expecting her first baby with him. She's non-committal so she's ok with not being able to move him in. Woot, that was no easy feat. I guess it was just down to me picking the right sim.