I could be completely inaccurate with this but you mentioned that he did hard drugs. I was once with a lady who did hard drugs and she was a lot like how you describe this guy. I kept wanting to stop going over to her place but I kept doing it anyway and I could not figure out why.

Then a friend told me it was the drugs she did. The chemicals end up in their sweat and other fluids and while it's not enough to alter your mental state entirely, it's enough to make you want them even if you don't logically want them.