Complex sentence: According to Riley, their friends, and Marlene Olive herself, she exerted control over Riley by threatening to break up with him or purportedly using witchcraft to influence him, and he was anxious to please her in order to continue the relationship.
Split into simpler sentences: According to Riley, their friends, and Marlene Olive herself, she exerted control over Riley by threatening to break up with him if he didn't do what she wanted, or purportedly using witchcraft to influence him. He was anxious to please her in order to continue the relationship.