Do you feel sorry for shantanu?

Yes he is correct to be mad. The curse that the Rishiji bestowed upon Vaishali would have probably been ovoided if she had ignored and loved Shantanu no matter what. It was the fear in her that caused her to take the step she did and that in turn is the reason for Shantanu's attitude and now the family's distruction. If she had not took that step and did all the poojas they do on a everyday basis now. things probably would be ok. She has caused this on her own. What she was trying to ovoid is really caused by herself.

Vaishali ended up caring more for herself than her son - she could have left the RP family and raised her son by herself if her love for the child was strong enough. That would have addressed any of fears she had from the curse and would still be justified as her love for both the RP family as well as her newborn.