Who is Radha? Well, Radha is both a devotee of Krishna and the one who is worshipped by Krishna, or you could also say Radha is Krishna and Krishna is Radha.
राधिकां कृष्णरूपं च कृष्ण राधो-स्वरूपकम्
Rādhikāṁ Kṛiṣhṇarūpaṁ cha Kṛiṣhṇo Rādhā-swaroopakam“Radha is the form of Krishna, and Krishna is the form of Radha.”
-Sanatkumār Saṅgītā, (a scripture attributed to the Divine descended Saint Sanatkumar)
Who is Radha? She is Krishna. Who is Krishna? He is Radha; Both are one, but appear in two forms.
This is a very important point. If you forget everything else I said on this day, just remember one thing: there is no difference between Radha and Krishna.
That being said, they still appear in two forms in order to do leelās (Divine pastimes). So just like Radha can have a leelā (Divine pastime) with Her brother and Her mother, She can have leelās with Krishna.
Sometimes people wonder, “Why didn’t Radha and Krishna get married? Krishna married Rukmini and all the other queens in Dwarika. Why didn’t He marry Radha?”
First of all, Radha and Krishna do get married in some avatars (descensions). They got married as Sita-Ram. Who do you think Sita-Ram is? None other than Radha Krishna.
And even when They come as Radha Krishna in previous avatars, sometimes They do a marriage leelā (Divine pastime) and sometimes They don’t. It’s of no consequence. It’s a matter of whether it’s decided to reveal that leelā for the happiness of the devotees, or in some avatars not. In fact, there are some descriptions of this avatar where Radha and Krishna got married.
There are unlimited leelās that happen. Just what’s written in the Bhagwatam is not all the leelās of Krishna. Just what’s written in the Brahma Vaivarta Puran (a Purāṇ describing Radha–Krishna tattva), or the Brahmand Puran (Purāṇ describing cosmic creation), or the Garga Saṁhitā (a scripture describing Radha–Krishna pastimes) - these are not all the leelās of Radha and Krishna. There are unlimited leelās.
