<p>Tl;dr, plus *old*…
</p><p>The person in the relationship has the obligation to curb any cheating. The onus was on Mako. Had he backed off from/after Korra's kiss, and laid down the "I'm with Asami" law, fine. But as it was, they were more concerned for Bolin's feelings having seen them than for Asami's.
</p><p>What made Mako cheating during Masami 2.0 was his not-immediately telling/reminding Korra they were broken up. By his own admission he wished it had not happened, so he let their relationship "resume" despite being with Asami. That <i>made</i> it cheating on his part.
</p><p>Granted, all of the Krew were stunted in some form or another. Korra, sequestered away; Asami, "daddy's little girl" who while society-socially adept was probably too interested in the company and learning the necessary skills to have a true social life; Mako, keeping Bolin and himself alive on the streets; Bolin, protected by Mako. But that does not excuse the fact Makorra was toxic. To Korra more than Mako, but that's the usual MF dynamic.
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