Sri Radha is called Madhava Sangini because Radha is so attached to Madhava that in any condition Radha will never give up Her sweetheart.
Once Paurnamasi tested Radhika love by saying:
“O Radha! You are just an ordinary cowherd girl. And Sri Krishna is so exalted and noble that even Laksmi-devi hankers for Krishna’s lotus feet. So Your desire to attain Krishna is like a dwarf wanting to catch the moon. It is an impossible achievement. So You should just give up Your attachment to Krishna!”
Radha replied, “O respected lady! Following your order I will give up My obsessive attachment to Shyama. But then You must also bless Me that now I can give up My body. Then by nightfall, I can reappear as a bumblebee to fly around the pure vanamala scented by the fragrance of Krishna’s face!”
(Vaidagdha Madhava)
By Mahanidhi Swami