I understand where you're coming from about TM. People like GBC do tend to pick someone they can get an ego boost from. With her he may have got his ego boost from her constant need to have him, she wanted him. Not being mean, but she is alot more plain to look at then the others, so maybe he hoped he could keep her where he wanted her and that she would believe his lies. But in the end she DID start making demands of him... so it went from him getting what he needed from her to her having the hide to ask for something back.
In the same way we see GBC has definite personality flaws alot of the clingy, needy people do have underlying issues aswell. Knowing how GBC is he would have played her insecurity for all it was worth.
In the end, I think no matter WHO GBC was with it always had to be about him. Either the whole "Look at me, look at me!" thing or "Keep this secret, i have an image to uphold."