Kol Mikaelson and Elena Gilbert left off in a gruesome confrontation. But after Kol is brought back from the dead right before the Other Side collapsed, things start to change between the Original and Doppelgänger.
Elena and Kol were together 10 years ago. They broke up because her friends and family hated him and she hated how he'd constantly let his family hurt him and abuse him so she ended it even though she really didn't want to. 10 years later they met again and everything changed.