Complex sentence: O'Hara based his fictional character of Gloria Wandrous on Faithfull, whom he had seen around speakeasies in New York City when she was alive, although he did not know her well.
Split into simpler sentences: O'Hara based his fictional character of Gloria Wandrous on Faithfull. O'Hara had seen Faithfull around speakeasies, although he did not know her well.