Devi Radha is one of the many expansions/avatars of the main Goddess Lakshmi just like how Sri Krishna is one of the many expansions/avatars of the main God Vishnu.

Radha, only got few years with him and an entire life of pain that spending away from that one person you love fills you with. That was the role given to her. That pain she happily accepted in place of attaining moksha and eternal peace just to spend few years with him.

Shrimati Radharani is actually Krishna himself. She is Krishna's feminine form. RadhaKrishn have one soul but with different bodies. Radhe is Krishna's Hladini Shakti. RadhaKrishn are one.

And, She is also an incarnation of Mahalakshmi. She is known as Goddess of pure Love and Devotion.

Actually she was born in Barsana. And she's daughter of King Vrishbhan and Mother Kirtida. Vrishbhan was the king of Barsana.

She incarnated on this earth with a purpose. To teach the world about real and pure love and devotion.

RadhaKrishn did their divine Prem-leela to teach the world about love. They spent their time with Sakhas and Sakhis. And also met near the Yamuna river.

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Radha was devoted to Krishna eternally. She taught us that Love is the base of Devotion. She loved Krishna eternally. Nobody in this universe can love Krishna like Radha. She was actually gone mad for him. Even a separation for a second from Krishna was equal to 1 year to her.

One day, Radha was expressing her love to Krishna. She was telling to Krishna about her love for him. She said to him that,You'll never know how it feels like when you are Radha. Radha can't bear the pain of separation from Krishna even for a second and starts yearning for him. And society insults Radha because she meet Krishna whenever he play his flute. Many people insults her by spreading rumours about Radha
And Krishna is like oxygen for her. If she's far away from him then she can't able to live".

Krishna was shocked after hearing all these things from Radha. He also wanted to know how it feels like when someone becomes Radha. He wanted to feel the pain of Radha. Krishna said to Radha that he'll become Radha and Radha will become Krishna.

Then Radha gave him clothes of Girls dress so that he'll become Radha. And Radha wear the peacock feather to become Krishna

Then Krishna was ready and he was looking like a girl. He thought himself is Radha and Radha was wearing his peacock feather so she became Krishna. Then he said to her, “I became Radha" Radha smiled and said,You only took external form of Radha but from inside you are not Radha. You don't have a heart of Radha. You just became Radha from outside but not from inside. You don't have Love for Krishna. Radha is that, who have love for Krishna only and yearns when she's separated from him. Do this fake Radha have a love like real Radha?She asked Krishna.

Then Krishna realised that nobody can become like Radha because her love for Krishna is beyond from this materialistic world. Even Krishna himself was failed to become like Radha. He realised that nobody can love him like Her. He surrendered to Her.