https://youtu.be/oOaljPw4aAM?si=33B9yHEnBJvJHZls
Don't know if makers think it out or not but, if Katha and Viaan had a relationship built on self respect only, (without that ONS) Viaan's reaction would have been a lot less violent. He wouldn't have shouted on his mother in front of everyone.
Viaan taking unconditional support for Katha should be in deep must be because only Viaan knows to what extent she can go through in order to save her loved ones. She went on with the night despite being very uncomfortable and traumatised and even after all that trauma, she kept her loved ones above all. No one else knows that except Viaan. And when someone questions integrity of that person, this will only trigger violence within you.
Any type of mutual respect love relationship in reality will not and should not compel you to shout on your mother who also, at all points was with you in your lives and you had such a deep friendship with your mother. This will surely raise a question in mind of Teji and Maaya about what kind of magic did Katha on him. But, that magic is related with a darkness.
If you think about it, the pain of realizing that you can't become a father again and realizing that your partner partially hid it from you is immense. But, it can only be countered if you remember that what this man did to her.... and to what extent she can go to save her loved ones and how much humanity is above her own personal biases, every pain seems feeble. Such realization can only make you see above your pain and look forward to live a life with this woman.
Without keeping that ONS in mind, Viaan just seems like a Joru ka Ghulaam. But, considering that ONS, all of Viaan's reaction make sense.
At this point, I am conviced that Viaan will be the one pulling Katha out of that dark night. He will not go in the shell. I am loving it already.