arnav's chacha framed arnav's dad and khushi's mom[they never had an actual affair]. arnav's mom couldnt bear it as she loved her husband very much, and , instead of trying to find the truth, she committed suicide![ so, asr gets the hasty decisionmaking bit from her]. Unable to fathom what his wife did to herself, arnav's dad too commits suicide.
this seems logical, because, then , when the truth comes out, dadi and khushi will be on one side as khushi will say that dadi's version is right and her mom was innocent!and , arnav will not be able to accept this for the following reasons, and hence , hate and separation track till babuji gets better and tells the truth:
1. arnav can never be wrong.
2. he cannot bear anything against his mom, so wont believe khushi.
3. he strongly believes that his dad is wrong.
4. he will not be able to bear that khushi is siding with dadi; and khushi will not be willing to compromise as her mother's honor will be at stake and she cannot bear that.
but , khushi is more sensible and , hence, might not hate arnav; whereas arnav being hotheaded will.
also, i think this is what mishti meant by saying that dad's role is OK OK. ofcourse, dadi doesnt know that khushi's mom is innocent[she will believe her son is innocent and khushi's mom framed him, not her other son] and thats why she keeps mentioning, woh aurat!
do i make sense ?