Korra was going to kill herself.
That’s what the slow motion shot of the tear falling off the cliff meant.
If she’s the avatar and she can’t bend she might as well die so there can be a new avatar.
Or else the world would be without an Avatar and there’d be another hundred year war.
So by deciding that suicide was a good idea she had given up all worldly attachments (including Mako) which was what Aang had to do unlock the Avatar State as well in season 3.