From what I can remember, the main leads are immortals that belong to enemy factions. The male lead's faction wore white or black or something all the time and the female lead's faction wore red outfits all the time. They met and fell in love somehow and were together even when they were doing their mortal trial. When they finish the trial, the guy loses his memory and is really pissed at finding that he is married to his enemy. He thinks she manipulated him or something. He later remembers everything and by then she has left to join and lead her faction into a fight. I remember bits and pieces of the drama but can't find it for some reason.