New Headcanon
Mako is at a fancy gala where Wu is entertaining dignitaries from all over the world. Among them is Lord Zuko, who, as usual, is not one for small talk, especially with stuffy lawmakers. He joins Mako along the wall, observing quietly. “So,” the former Fire Lord begins after a few minutes, “what’s new in your life, Mako?”
"I just found out both of my exes are dating each other."
Stunned silence.
"That’s rough, buddy."
I don’t want to live in a world where this isn’t 100% what would canonically happen. And luckily, I don’t have to.