I really dont think that Mai was, or ever will be, truly in love with Zukoat least, not the Zuko that the Gaang knows. Shes really more in love with the idea of Zuko than anything else. Zukos changed so much. Mai has no idea how much he has changed. Note the following quotes (The Beach and The Boiling Rock, respectively):
For so long I thought that if my dad accepted me, Id be happy. Im back home now, my dad talks to me. Ha! He even thinks Im a hero! I should be happy, right? But Im not! Im angrier than ever and I dont know why!
Because Im confusedbecause Im not sure I know the difference between right and wrong anymore.
Zuko
The truth is, I guess I dont know you.
Mai
Mais right in that respectshe doesnt know Zuko. Shes unaware of what hes gone through and what hes had to endure. Shes just had to obey everything her mother and father told her to do. Compared with what happened to Zuko, that sounds like a spring meadow with dancing bunnies. Zuko was banished from his home by *his own father*, who never really loved him or Azulato quote him in The Beach, when he flips out at Ty Lee:
*Bad skin*? Normal teenagers worry about bad skin. I dont have that luxury. My father decided to teach me a permanent lesson on my face!
All Mai really seems to love about Zuko is the child she had a crush on, the child who was happy being where he was. He was too young to know or care about the war, and ignorance was bliss, as it always is when you are that young. But that child was severely wounded when his motherone of the few people who actually cared about himleft him and his family, and that child later died, along with a third of the outer layer of skin cells on his face, in the Agni Kai arena. She assumes that that child is who he wants to be. Not so. After Zuko came back from the war meeting talking about how hed sat at his fathers right hand, Mai seems to think that was all he ever wanted.
Oh, Zuko, thats wonderful! You must be happy!
During the meeting, I was the perfect prince...the son my father wanted. But I wasnt me.