In that scene, while most movie goers probably thought he was being his manipulative Joker-self, he seemed to be asking Harley to be his submissive.
Joker: Would you die for me?
Joker: That's too easy. Would you live for me?
Joker: Careful. Do not say this oath thoughtlessly. Desire becomes surrender. Surrender becomes power. You want this?
Quinn: I do.
In the SS, through flashbacks, they show Joker's sadism and Harley as a willing, masochist participant. Their power dynamic, in the film is pretty decent in that they worship each other And while the introduction of this type of dynamic pissed off a LOT of die hard fans as not being true to the comics and their actual, abusive relationship, I, for one, was very grateful that David Ayer gave us a newer, better version of the Joker-Harley relationship. I'd rather see Harley be wanted, protected and needed as a sub as opposed being a punching bag and punchline for comic fodder. Harley Quinn is such a complex character who deserved so much more than being a sidekick who suffers abuse from a douchy boyfriend.
Intentional or not, this is, of course, how it appeared in the film.