I don’t understand the prince louis storyline ending

okay so i’m on episode 17 s5 of gossip girl and im confused, was louis supposed to be evil/lying to blair the whole time, or did his feelings change after the tape was sent out of her confessing to chuck?? like im pretty sure he already knew she loved chuck so why would that be the turning point lmao,, i understand he had moments of deception and scheming but it was mostly justified considering blair’s constant lying and cheating on him, so was his plan to fake marry her from the beginning or just at the end?