Complex sentence: Ryder agrees to no longer romantically pursue Marley now that she is dating Jake, and, in retribution, Jake helps Ryder be selected as one of the number's lead dancers alongside Sam Evans (Chord Overstreet), despite being a better dancer than Ryder.
Split into simpler sentences: Ryder agrees to no longer romantically pursue Marley now that she is dating Jake. In return, Jake helps Ryder be selected as one of the number's lead dancers alongside Sam Evans (Chord Overstreet), despite being a better dancer than Ryder.