Complex sentence: Quinn becomes sincerely interested in pursuing a relationship with David, but is ultimately rejected because he still sees the shallowness to her personality, though he does admit to seeing more depth in her than in her friends, the other members of The Fashion Club.
Split into simpler sentences: Quinn becomes sincerely interested in pursuing a romantic relationship with David, but he turns her down because he still sees the shallowness to her personality. He nonetheless says that Quinn has more depth than her friends, the other members of The Fashion Club.