I do agree that Dev's share of mistakes is greater than Sona's. But what also needs to be kept in mind was that none of those mistakes were intentional. He did not reveal about prenup and about sona's infertility,two main reasons why they broke up because he did not want to hurt sona. And when sona did not understand that and left him, he deliberately hurt her, as though punishing her for leaving him. I agree that dev was one of the most selfless characters in the show. But he was flawed and perfectly human.
Sona's character was the best until the reunion. She was perfect for any being. Post reunion, they just butchered her character imo. They tried to show her too mahaan and and they also did it to Dev's character role reversal track onwards. Thats where makers faltered, they lost touch with the very essence of the show which was its relatability. And no, i will not say that sona was selfish just coz she kept soha with her and didnt meet dev. She had her own reasons, she tried patching up with him 6 months after soha was born. But was snubbed. So her already hurt ego was bruised a little more. Both dev and sona post this separation track just held on to their egos, not willing to relent until soha intervened. If sona was selfish, she wouldnt have let soha bond with dev once she came to know he is her father. She wouldnt have tears of joy when she heard soha call dev papa, in her eyes. She wouldnt think about getting sisters back after getting back with dev after 7 long years. She wouldnt have let ishwari meet soha when she came to fight with boses when soha was sleeping. After all that she went through in ishwari niwas, being treated like an outsider with no say in some of family"s major decisions, like riya's wedding,neha's divorce, being forced to undergo fertility treatment for ishu's sake, being lied to about prenup, her father being slapped by her husband(even if accidentally), being thrown out of her own house supposedly by her own husband...for a woman who has gone through all of this,i think it is a little fair that she keeps her guard on and is slightly possessive about her daughter who was her only source of support for 7 long years. Yet she never restricted soha from bonding with dev,she solved the khatri matter, she did a lot for ishu's family even when she had no intention of reuniting wuth dev. And that can never be selfish.
Both dev and sona were wonderful humans with some very basic human flaws which do not get them crucified. But their biggest flaw was letting ishu and bijoy control their relationship. Both ishu in bijoy in their love for their children and somewhere their ego always kept Devakshi's happiness secondary. And that is what ruined everything.