It is hard truth of life that for making relationship, it require two people consent but for breaking relationship only one people consent is enough.
You can say Viraj is selfish but Viraj and Teji relationship was not working for sometimes, probably years. They might be staying together only for Viaan and Teji one sided love. When seema entered into Viraaj life, he thought he also has the right to live happily rather than staying in bad marriage. Things don't go well, of course Teji is of no fault. More than 16 years of marriage, no woman will be able to digest it. What Teji did is to use her child to force Viraj to come back. Again Teji is no wrong. While Man has money to offer to his second wife, woman at Teji's age has nothing to offer to new husband. The best possible way is to emotional blackmail Viraj that if he left, he will not be able to meet his son.
Viaan should understand this after all he also not able take No from Katha. Viaan did a grave mistake in his life at the age of 32-33. What Teji did is nothing in front of what Viaan did. Instead Viaan is blaming Teji for his own grave mistake. He think what he become is because of mother. That's not true. Teji never taught Viaan wrong thing. He never taught Viaan to disrespect woman. Instead she opened NGO especially for women. What Viaan did to Katha, it is his own thinking. No one is responsible for his ONS offer other than himself. It is said if a person under 20 do some mistake, half of the responsibility goes to parent. But Viaan was at his 30. 10 year is enough to change ideology and personality. Viaan was 15 when his father left Again this is not tender age which would affect him so badly that gives him traumatic experience. Viaan should not blame Teji for his own mistake.