They've been married for a month! Haven't they banged yet? It should solve most misunderstandings since chiyo would show her true colours...
If I remember correctly it was an arranged marriage. They probably haven't even kissed. He probably hasn't broached the topic because he is a gentleman and most likely doesn't want to pressure her. Especially since he thinks she dislikes him in some way.
She wants to be seen as a good wife which seems to mean not showing interest in sex. So she's not going to bring it up.
What needs to happen is that he needs to ask her what he needs to do to improve (since he is under the impression that he is lacking in some way) and then confront her on her strained smile when she inevitably tells him (truthfully) that he is fine the way he is. That should trigger her admitting that she is the imperfect one because she has "impure" desires.
That will not happen for some time cuz the comedy comes from their misunderstandings.
I want mooooreeeee!!!
And I also want more evil Iruma!!!