Complex sentence: Chandler tells Monica that he will divorce her if she does not disown Ross, which would humiliate her; later, Ross tells Monica (untruthfully) that Chandler is having an affair with Phoebe, which Monica believes.
Split into simpler sentences: Chandler tells Monica that he will divorce her if she does not disown Ross, which would humiliate her. Later, Ross tells Monica (untruthfully) that Chandler is having an affair with Phoebe, which Monica believes.