Complex sentence: This is because of the three sisters, she was closest to Phoebe, even though Paige was her whitelighter, & because Phoebe was the one who was always there for Billie and always saw the best in her.
Split into simpler sentences: This is because of the three sisters, she was closest to Phoebe, even though Paige was her whitelighter. This was because Phoebe was the one who was always there for Billie and always saw the best in her.