From the precap and from spoilers and all I feel that Sid is aware of both sides to the story. There is never one side to anything. Sid clearly asks Roshni in the precap if she does not want to know...from that to me it seems that whatever DD and the rest of the Patels believe to be Shiv's wrongdoings is not all true or accurate. I feel there was a major reason for Shiv's actions. Not sure if one child dying could have been the main reason for them to be separated.
I am thinking that Shiv was forced to leave DD and the rest. Either by someone or because of some serious reason. He probably thought DD and his family would be happy without him or something. Then maybe he had found out that they were doing well without him for so long that he never tried to keep in touch. Maybe he did from afar all those 23 years but never showed his face. Maybe he promised to never show his face to them, which he kept. Similar to SidNi. Sid was forced to leave Roshni so DD could get her house and business back and had promised DD that he would never show his face to them again.
The only difference between the two is that DD or anyone else never tried to find out the truth about why Shiv had really done what he had done. There was no trust or faith there..but as for Roshni, she believes with 100% that Sid had a solid reason for his actions and has made it her mission to fight for him and not give up on their relationship. She was even ready to be poor again for him if it meant being with him. And Sid seeing Roshni's attempts and her not giving up he too got the will power to also fight to be with her again and keep her family happy.
I do think Sid knows what Shiv did as well as why he did it. Sid will be patching them up as he had done DD-Roshni.
Whatever it maybe...I am sooo excited to see how things play out in the show. So many possibilities and so many ways that this track could go.