Complex sentence: Chandler knows Monica doesn't want to leave New York so he arranges to have a four-day work week, so that Monica can stay in New York and Chandler can fly back to see her on the weekends.
Split into simpler sentences: Chandler knows Monica doesn't want to leave New York so he works it out so that he will only have to work four days a week. Now Monica can stay in New York and Chandler can fly back to New York on the weekends.