He lost Sai once. And he was living an empty life. He had Vinu. But look at them as individuals. Sai missed V, but she was still leading a much better life than him.
The key lies here. You mentioned that people mature, with age, with roles and responsibilities. But there is one major difference between Sai and V. For Sai, her kids come before anything. She will sacrifice anything for them, even V. And she did.
For V, Sai comes before the kids. What we are seeing right now is just that. The kids are unable to make him break away from P. He knows the kids are suffering in this bargain, yet he is risking them for P's sake. Which is wrong. But till now the biggest threat has no hit him truly. He knows Sai cannot love anyone else, and this is the trust he gained post leap. So he is heavily depending on this realisation. That is where his confidence lies. But if you revisit the difference I spoke about in their characters, his whole life will shake if he loses Sai. He hasn't encountered that risk. This is what the new entry is here to do. Reality check. He can lose Sai. Can he afford it? That is the question now. While the kids could not break him, will Sai be able to break him is what we have to see.
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