maybe Heer got the custody papers from lawyers,then she went to Prem and showed how disgusted she was at his act,then maybe Prem will be shocked and would go to Gayatri and would make the misunderstanding clear in front of Heer and would tell her that he can never think of anything like this and if he wanted anything as such,he would have done it long way back..maybe then Heer would realize her mistake of saying bad things to Prem regarding custody thing..then Prem may clear his part about cheating his wife 6 years back to Geet which would lead Geet to carry on with the mariage thing and make Prem's point of view of that night clear in Heer's mind(maybe when her best friend explain her,she would understand better)..then she may regret her acts about bad-mouthing Prem and thinking so low of Prem,../then this sangeet thing comes where Heer feels bad seeing Prem with someone else ...(I may be wrong,..this thought just came to my mind so shared it with you)