To kill his master, Leo knew the idea wouldn't be so simple.
Firstly, Leo still craved draining every single human like the monstrosity that he was. This held him back at times, and it was the reason he hadn't reached out to any of his friends since calling Chase that one time.
They were good people, even Esme, who always thought of herself as a demoness. After meeting Kari and Scarlett, she was far from a demoness—not that he ever needed to compare them. Anyway, his friends would help him; of course, they would, but first, he might attack them, and second, if the first point wasn't enough or they did not die by his hands, his friends would also wish to save him.
Leo did not wish to be saved. These cravings to drink and kill humans also made him crave death. This was not a life to lead. Even if he did get these cravings under control, he couldn't live as a vampire.