Complex sentence: In the end, Sebastian stays with Danielle; professing his love for her, only to find that she does not reciprocate, but is in fact working alongside Kathryn in a secret plan to dupe Sebastian.
Split into simpler sentences: In the end, Sebastian stays with Danielle; he professes his love for her, only to find that she does not reciprocate. It turns that Chere is actually working alongside Kathryn in a secret plan to dupe Sebastian.