When Sona went to the kitchen, all he was worried was for her. He was only concerned about her. He didn't pay any attention to that ring and went straight to the kitchen to make sure Sona is not in pain and when Sona couldn't control her emotions and told him. Its hurting her, his reaction was i knew.
Even when she was devastated from inside she was worried for his health and asked him how is he feeling now. He shared to her that he's not well, he doesn't feel like eating anything. He has tried everything... And Sona thought its just the case of acidity. No Sona... He's in love with you darling and just the thought of his engagement is making him restless. She made him drink something so that he'll get better and he obeyed. Just to be with her makes him feel good and this what he needs to understand. And the day is coming when he will understand everything.
Now the highlight of the scene. The way Dev turned to look back at Sona. His eyes were speaking. It looked he was thinking why he feels good when she is around. He forgets all his worries just talking to her. There was some kind of longing in his eyes.