Complex sentence: Janine comes to believe in Kate and Jed's feelings for each other but Molly is still dubious, eventually attempting to prove Jed's faithlessness by seducing him, which fails but angers Kate to the extreme.
Split into simpler sentences: Janine comes to believe in Kate and Jed's feelings for each other. Molly eventually attempts to prove Jed's faithlessness by seducing him, which fails but angers Kate to the extreme.