Complex sentence: Cooper reunites with Diane, and with Diane and Cole goes to a room underneath the Great Northern hotel, and after using the key to his old room is taken away from our reality to meet again with MIKE and Philip Jeffries.
Split into simpler sentences: Cooper reunites with Diane, and with Diane and Cole goes to a room underneath the Great Northern hotel. After using the key to his old room, he is taken away from the Earthly plane to meet again with MIKE and Philip Jeffries.