Rightly or wrongly that boy felt he was less loved by his father.Well Jagya didn't love his son Abhi any less. But it was also true that Mannu and Shivam found him more accessible than his own son partly because of Abhi's personality and partly because Jagya did not communicate well with Abhi.
If Abhi didn't feel insecure he would not have had issues with Shivam.
Shivam was being spoilt by Dsa and indulged by Jagya because he felt that he should be kind to that boy who is fatherless. The first scene between Abhi and Shivam was when they both were babies Shivam took Abhi's toy. Abhi wanted it back Ganga and Anandi jumped in.
Anandi took the toy from Shivam's hand gave it back to Abhi because she felt he will start believing that he has rights over Abhi's things. Ganga felt Abhi being older should let Shivam play with his things.
This could have come out of compassion for that baby who never saw his father and now had come to live with strange people.
So it is quite easy to understand how things went by in 11 years compounded by their personalities Shivam's extrovert personality and Abhi's brooding and introvertish personality.
And one more thing I don't think Anandi left BH because Ganga made things difficult for her but she believed her stay is making things difficult for Ganga. She never liked staying there anyways.
Anandi did take the decision keeping her son's future and her relationship with Singhs in mind.
Shivam was showing all signs of DSa's ladesar Don't think Anandi wanted her son to become BH ladeser because he is not that.
Well Ganga's methods of handling problems may not be right but her problesm are real and so are Abhi's problems.