Lord Krishna (apparently) left Vrindavan at a very young age along with Lord Balaram. All Vraja-vasis experienced intense Viyog (separation) because of that. Krishna also felt the same Viyog from the Vraj-vasis. However, Balaram could not experience the same as Krishna always kept Him by His side. Not could Krishna experience separation from Lord Balaram like He felt from other Vraj-vasis. Hence, when Krishna came as Gaur, He fulfilled this desire also when He went to Puri along with His desire of relishing Radha-bhav. He sent Nitai to East Bengal for distributing Krishna-prem to one and all. And here in Puri, He experienced intense separation from Nitai. Simply by chanting Nitai’s name He would fall unconscious on the ground. And the same happened with Nitai when He was away from Gaur. He would shout “Aha re! Gauranga!” and He would fall down on the ground drenching His body with His own tears.
So this is a secret desire of both the brothers which got fulfilled in this Lila. In fact, in this most confidential Nitai Gaur Lila, the innermost desires of the Lords and all the associates got surprisingly fulfilled.