When Mihir came back from the wedding, his mindset was that he thought he was being unfair to both Tulsi and Savita and he just wanted to set things straight..and what does he find on his return?
When he sets foot inside his house, he is greeted by his mom's dead body! Now imagine what a horrible jolt that must have been. Just like Karan is ready to do anything for his mom, Mihir really loved his mom just as well! But in contrast, Mihir always learnt to strike a balance between his mom and his wife which Karan, sadly ,could never learn to do. Karan was blinded by his love for Tulsi and even her wrong-doings were praised by him!!! It was totally ridiculous!
Coming back to the topic, it was really bad the way Karan behaved with Mihir. Agreed that Mihir did a great mistake, but that was 20 years ago- Mihir has never harboured any bad feelings against Karan even though he's been misbehaving with him for the last 20 years- so why cant Karan juts come in terms with reality and try to look at things in an unbiased way? This is really going too far and this is no way to talk/behave with your father, no matter what!