Complex sentence: He tries to catch her as she leaves but is brought up short by Rebecca, so he ducks out of the trip and embarks on an obsessive search for her, and the story of Matt and Lisa's romance unfolds in flashbacks.
Split into simpler sentences: He tries to catch her as she leaves but is brought up short by Rebecca, so he ducks out of the trip and embarks on an obsessive search for her. The story of Matt and Lisa's romance unfolds in flashbacks.