So, as you guys may be wondering, even though Radha is married to another person she still love krishna. Isn't that worng? Well it is not. Why you ask? Let me go into detail.
First, The husband of Radha, Ayan is a bad person sent by Kans ( The antagonist ). He was a very Arrogant and somewhat lustful. Ayan and Radha had to marry because of certain reason and after marriage Radha rejected to have any physical relation with Ayan as she was in love with Krishna. Yet she said that she will do everything a wife should do except any physical relation. So Radha didn't even loved Ayan in the first place.
One time, they went to ashram of Sage Durwasa. There, Ayan tried to feed Radha a fruit (given by Kans), which will make her lose mind and become lustful. Then Radha thought that before eating, she should offer it to the sage Durwasa as she didn't knew the truth of the fruit. But Ayan was not patient enough and had a fight with Radha.
Next day she was crying sitting on a rock when, Sage Durwasa who was mediating, woke up from his meditation because of the noice of crying Radha made. Sage Durwasa was known because of his anger and giving curses in the anger so everyone were sure that Radha would definitely get cursed.
He went and saw Radha crying. After he saw her, he realized who Radha actually is, goddess of love. He was about to join his hands to show respect but Krishna, the avatar of Vishnu told him that he should not show respect as both of them are in thier human forms and Radha too didn't knew that she was a goddess.
Sage Durwasa then acted and angrily asked Radha the reason she was crying for. She told the sage everything and the sage got angry. He then angrily asked Radha to eat the fruit which Radha did but it didn't had any effect. Ayan was shocked to see this while Sage Durwasa explained that he knew what the fruit was but he wanted to test Radha. Ayan who was sweating, thinking Sage Durwasa might have realized the truth, had a sigh of relief.
But what he didn't knew was that Sage Durwasa already knew about the fruit and he became angry again and told the truth to Radha. He then cursed Ayan that the emotion he had while giving the fruit to Radha, if he ever touched Radha with that emotion, he will be burned to ashes. After that, Ayan broke every relation with Radha but still acted as a couple because of the society.
Second, the love of Radha-Krishna was very sacred. They both were born to teach the world about love, the purest form of love. One of many reasons Krishna was born was to teach about love. How in true love, one does not need to be involved physically as their soul is already connected. And even after Radha was married, the care they both had for each other was next level.
Third, Kans sended Ayan so that he can take Krishna's shakti ( power ) as it is believed that everyone is incomplete without their better half and gods too are incomplete without thier better half. A girl or a goddess is considered sakti. This is drived from a saying
"Shiva is incomplete without Shakti"
Meaning that the God of Destruction, Shiva, who has the ability to destroy the universe itself is incomplete and powerless without his wife, goddess shakti (power).