Why the devotion to bhabhi-ma ?

Kostins:

1) Why does Yug call his bhabhi , bhabhi-ma ? There is no large age gap between them and its not like his bhabhi raised him or something. Yug’s mom is very much alive and present. Usually bhabhi-ma is used if the bhabhi is much older and a maternal figure. 

2) whats the reason for Yug’s devotion towards his bhabhi ? Its really quite cringey and forced the way they both keep harping on how much he loves his bhabhi-ma ! I get that Rupa played a role in saving Yug’s mom during a fire incident but surely thats not the only reason for his constant focus on her ?

The first reason was that she saved her mothers life. I think Yug’s mother was taking her own life and that’s when Rupa saved her life. That’s why Yug hates nachnaywaliyan.

second he is super family oriented like he goes blind for protecting woman in the house and gets all unbearable for anyone who comes in their way.

Plus they grew up together.. what I don’t understand is that they showed that kahani was 4-5 years old in the car when it went down. It also seems that Rupa and Gunjan are older than Kahani in the present. Its so confusing. Whether Rupa is older than Yug and Kahani but if Iravati is Kahani’s father’s second wife so rupa and Gunjan should be younger than her. Its super confusing!