My understanding is Julie already had the pills. After Jeremy found out he asked for some.
Julie talked Jeremy out of the drugging, house burning idea. Saying there were valuble uninsured items, it would be difficult to set such a big house on fire & someone might see the big house burning. Jeremy also realised the pills were not strong enough after trying them.
Adam, wearing my counsellor cloak, I can only tell you that IF Julie said what YOU are saying she did, she was actually giving him permission to look for another way of doing it because NOWHERE have you said that she told him how wicked a thought it was and if he mentioned it again, she'd leave him. OH. She couldn't, could she, because SHE'D provided him with the sleeping pills.