In Part I, Fujino continuously emphasizes that Asuna has this maternal instinct to take care of the weak, although some lines are crossed. This is Asuna's strength and also her weakness, and Inoda takes advantage of it. So in all it makes sense.
But in Part II, such SAO background has gone a lot, especially Asuna's and Kirito's characteristics. Like you said, making out in the virtual game. But Asuna and Kirito spend so much time together in virtual games, I believe that the virtual games should have become another realities to them. So Asuna believes that having sex with Inoda in FOG is not cheating? Just think about it.
I understand that Fujino has to come up with a way of pushing the story forward, but personally I think this idea (starting to corrupt Asuna by doing virtual sex in FOG) is not a very good one.