You bring up a good point. She was more dismissive of him at certain times in her life. However, I am not so sure she was completely sober then either. Perhaps she was just more sober.
I think HKS was in love with her. He was probably obsessed with her.
Have you ever been around a drug addicted person or alcholic. Addiction is a strong thing. Try to take away their fix and you may get booted out of their life.
So in his obsession, he supplied her the drugs to stay in her life because he might have lost her if he tried to take them away.
Precisely. A happy, healthy, well-adjusted Anna, would not have needed HKS in the end. It was in HIS interests to keep her "unhealthy." Sick.