Well, maybe Asuna is STILL the "NTR" tag, and Kirito is the "Cheating" tag. Plus it's about perception. Kirito secretly ignores the fact that he is actually cheating on Asuna. He helps with Sinon's problem, Suguha helps him relax, he helps Klein with his fetishes, but he does not consider it treason in any way.
And to be honest, what Asuna is doing in the game with Inoda is no longer NTR. She's fucking Inoda quite voluntarily. Technically, there is nothing left of the concept of "theft". There is only the real world left for the NTR tag, but I can assume that Asuna will come to this voluntarily in the real world.