You didn't say she didn't have a right to be hurt, no, but you did say it's "Not really a betrayal on her [Noriko's] part" and his comment was in direct response to that.
Nothing you've listed here address any of his points and none of them reinforce your original statement.
And no, the fact that she expressed a desire to fuck him openly - usually in exaggerated ways that Niki always obviously took as jokes - does not remove or even minimise the betrayal.
If you personally don't feel bad for her then that's whatever but there's no argument to be made that Noriko didn't betray Niki or that Niki has no cause to hold it against her because both these things are blatantly untrue. You can argue that Niki should recognise that Noriko was groomed and should ultimately forgive her/not hold it against her forever but that's it.