Yes. That is true. Life is tough. As you say, we have to accept that past is past and live in the present. But since in reality we have no other go, atleast in fiction we would like them to unite and live a happily ever after, that is why all this bickerings with you.
Ofcourse we will have to accept your decision that they have become two families now and to be honest I don't like Karthik being upset too. But I cannot say that for Brindha as she is the one who was responsible for their separation, if not the sole one. If she had wanted she could have helped Sudha and Kannan get together. So I have no sympathy for her at all.
