Kesar's voice over was impactful. Gulaal read that in a hurry. What we heard in the episodes where Kesar was silently suffering by finding company or thrashing his own frustrations with the help of one of those letters.
When Gulaal came to Kesar's room to leave those letters, Kesar was just concerned if she has read all those letters. He was least bothered about how or when or through whom the letters reached her. He confirmed what he had confessed before that he was not just fastened to her from childhood; he has been in love with her since childhood too.
The amount of hurt was evident when she brushed it aside and confidently said that IT IS NOT LOVE. When she labels it as "attachment", he is more hurt and his eyes well up immediately. He comes forward to tell her she can convince herself in any way but not to belittle his love calling it as immaturity.
He makes it clear that he has loved her and HER ALONE in all these years and one day she will have to understand the truthfulness in his love. When she felt there was no point arguing, she left and Kesar was again hurt due to her rejection.