Yash has see real and raw Aarti more than once himself, she didn't lie when she was caught with him and could have stayed out of trouble but she never shied from truth.
He wants mother for her daughters, he saw pure mom in her. Who was tired, distressed and angry but still one look at her child calmed her down. She forgot all her pain and just melted in those moments with Ansh.
She didn't create scene in front of all in party, she is woman with dignity and respect.
What else he wants, if he still even have iota of faith in what Bua said then plain and simple he doesn't deserve her.
But then I doubt that he will believ her, he is sensible, he gets angry fast but still haven't shown it Aarti as he knows he is at fault in their MU equally.