How beautifully you have described one of the most important phase in their lives. It was short, maybe not even dramatic but it was very impactful. That wasnt just a sip, rather it was a deal silently sealed among them. I am glad that Kalpi was the first one who took a step forward towards that deal and made Raghav's everything her own. It was a promise from her heart that she shall be on his side always. She shall share his goods & bad, ups & downs and all of his happiness. And together, they shall conquer everything!
And Raghav's reaction was equally beautiful. The way he just stared in shock was because he wasn't expecting Kalpi to reciprocally do what he did for her. And in the end it gave both of them inner peace.