We are a product of our upbringing and our circumstances.
Dev grew up in dire poverty enveloped by conditional love but more importantly a strict sense of never ending responsibility. His mandate was Be successful so that we can all be successful. He defined what success was. To him success was winning in the first instance come what may. His background meant he didn't get second chances.
Sona had a middle class upbringing enveloped by unconditional love and a strict sense of responsibility too. Her mandate was Be independent so that you can face this world. She defined what independence was. To her independence was having the confidence that when she brings up something with her loved ones they will support her. Support however isn't blind. She knows she will be called out for when she is wrong and she knows she should do the same.
They are both the sole bread winners of their family. Dev however asks his family "what do you want?"... Sona asks them "How can I help you?"... You see the difference... they both facilitate happiness around them differently. Their circumstances and experiences make them different.
Let us remind ourselves, how this super strict nutritionist isn't able to portion control what his brother eats. In her words, you are different with your own family. This is what Dev is struggling to make Sona understand in case of Neha. He knows he isn't doing the right thing in the long run and he knows Sona is Miss right (his words on dev ki diwangi night)... He however doesn't have the strength to fight the multitude of emotions that Neha is presenting to him.
I won't even call their love mature. It's anything but mature. Love is like wine. Takes time to mature. What it is is its predictable. They can both now predict how the other will react. Sona now knows that in uncomfortable situations she will not be able to ignore the quick fix solution and Dev won't be able to deal with the questions she will put to him. She knows Dev will (obodhro-rily) blank her out by yelling at her. Dev now knows that if he needs to deal with the tsumani of (usually unreasonable eg Honeymoon cancellation) expectations of him, he needs to keep Sona out of that storm. He is at the vortex and he knows he needs to let that storm pass before allowing Sona in... Because she is the one who will nurse the wounds inflicted on him by that storm. At a sub-conscious level I feel now they both know that. For healing to happen, I am banking on this assurance and mind-set that they share.
They are not opposites... they complement each other.
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Edited to add on 8th Nov
Dev, spot the difference. Do you see how Sona has a plan of action to solve her brother's problem? She took stock of the situation, looked at the strengths and worked on a plan. Wish neha had a sensible sibling too.
Neha, spot the difference. Do you see how Dev and Sona are trying so hard to patch up? Sometimes it's Dev other times its sona. It's a balance.
Ishwari, spot the difference. Papa Bijoy pushed his daughter and son in law to sort their differences. He didn't say "my daughter is precious and she doesn't want to talk to her husband so I will not allow her husband near her"
Dixit sisters, spot the difference. Sona opened her brother's gift and appreciated you. You simply ran to your room without paying a minute to appreciate what bhaiya got for you.
Sona, spot the difference. Dev is trying hard to integrate in your family. Give him credit but stand your ground. Don't just pout. Explain to him how his rudeness hurts you