Complex sentence: Deflated and disenchanted with his profession, he becomes a bicycle messenger for a service, Kurtzweill's Quicksilver Express Co., Ltd. Jack deals with his parents and his girlfriend, who are disappointed with his job as a messenger.
Split into simpler sentences: Deflated and disenchanted with his profession, he becomes a bicycle messenger for a service, Quicksilver. Jack must deal with his parents and his girlfriend, who are disappointed with his job as a messenger.