Complex sentence: He begins flirting with her, telling her he must have been a fool to let her go, she says she's the fool for she booked her ex's band for her sister's wedding this coming weekend.
Split into simpler sentences: He begins flirting with her, telling her he must have been a fool to let her go. She tells him she was a fool because she booked her ex's band for her sister's wedding this coming weekend.