You didn't get my point. You invoked the disapproval of "society" to invalidate any reason Hikari would be justified to get in an affair with a married man.
Who is that society that has the right to judge her reasons? Even Moe doesn't judge.
As for the wife, her hurting is, as far as we know, totally virtual: what she doesn't know doesn't hurt her (and obviously, the manager doesn't intend to divorce). If anyone is hurt here, it's Hikari herself, but since it's self-inflicted and she's an adult, you still don't have the right to judge.
My point is, Hikari has one or more reasons to be in that relationship. We may think she's mistaken and that she should get together with Moe, and were we her friends, we would probably advise her to break that relationship because it's actually hurtful to her (and possibly to the manager's wife). That's even what Moe tells her.
But you shouldn't judge her to be an horrible person just because her moral code isn't yours.