Sumi and Mesh I think we shouldn't be too much worried about Naina. There is no place for some serious "romance" or something like that. I think it will be more Suraj doing cute things to impress her. After all she is Colonels daughter and, if you saw in that olv her meeting with Chakor, her guards didn't let her interact with Chakor too much. I think she was even standing behind them, like seriously, girl wanted to help other girl but just in case guards should be standing between them. What I want to say is I doubt there will be serious interaction between Suraj and her like "romance" etc.. she will fall for him probably on her own, Suraj will probably just try to do things which will impress her.
I agree that deceiving someone, breaking someone's heart intentionally is unethical. But it serves for greater purpose. In July 2017 Chakor lied to Suraj, broke their engagement and his heart for saving village kids. And she loved him. I don't remember anyone questioning that. Now, they will lie unknown girl, maybe brake her heart, for saving nation. Suraj doesn't love her. There are subjective differences between last year and now, but the message is almost the same.
And trough all this, however it turns out to be Sukor won't be shown as villians. Am confident in that. They will find a way to make this with the less possible hurt for every other character. Because we all know in TV show if someone is to be hurt and empathised with that are leads.