Complex sentence: After DoodlePants defeats him, Spongebob realizes that Doodlebob created Doodle Bottom because he was very lonely, so he erases his mean face and turns him happy, then Spongbob, Patrick, and Squidward leaves the now happy Doodlebob and Doodlepants stays behind to keep Doodlebob company.
Split into simpler sentences: After DoodlePants defeats him, Spongebob realizes that Doodlebob created Doodle Bottom because he was very lonely, so he erases his mean face and turns him happy. Then Spongbob, Patrick, and Squidward leaves the now happy Doodlebob and Doodlepants stays behind to keep Doodlebob company.