Actually, if you see, Meerabai didn’t choose Krishna as Her lover after She married King Bhojraj. In Her life history, it is stated that during Her childhood, She saw a marriage procession from Her palace going on. She, out of curiosity, asked Her mother, “Who will be my bridegroom?” Her mother said, ‘Lord Krishna Himself will be your bridegroom.” From then on, She considered Krishna as Her husband and not just lover.
She Herself, in Her keertanas, answers this question as to why She chose Krishna over King Bhojraj. She says:
Raane var raa kai paraniju janam janam mar jaaye
Var Paranijo Saanvaro mhaaro amar chudo hoi jaaye…
which means “Why should I marry Raanaa (Raanaa Bhojraj)? He is a human being; hence he will die one day or the other. After that She would be a widow. But then, if She marries Lord Krishna (Saanvaro), then She would be Nityasumangali (ever-married to Krishna) or Nityasuhaagini since Krishna is eternal and blemishless.”
She specially worshipped Giridhar Gopal, which is the roopa of Krishna when He lifted the Govardhana Parvata. Traditional biographies of Mirabai narrate that She was an incarnation of Madhavi named Gopika stree. She was married to Krishna’s friend Sridama. Her mother while the time of vidaai, had said, “There is a cowherd boy in Vrindavan by the name Krishna. Stay away from Him because He is very, very attractive. If you even see Him once, you will be attracted to Him and will forget your own husband. Therefore, even if He asks you to show your face, don’t show Him your face.” And thus, obeying her mother, Madhavi came to Vrindavan after marrying Sridama.
Krishna saw Sridama and asked Madhavi to show her face once. But She didn’t show Her face to Krishna. But then, when the Govardhana Uddharana (lifting of Govardhana Parvata) took place, all the Vrindavana-vaasis had come there under the Govardhana Parvata. Krishna had lifted it on His little finger. Maadhavi Gopi too had come there, but then She couldn’t see Krishna. Krishna was blurred to Her. Since She had refused to show Her face to Krishna, now Krishna was blurred to Her. She yearned to see Krishna. Krishna then said, “You will be born in Kaliyuga as Meera. There you would worship this form of mine by the name Giridhar Gopal, and then you would get my darshan.”
As per Krishna’s words, that Madhavi Gopika stree was born as Mirabai in the Rajput family in Rajasthan. Though She wasn’t willing to marry, She was married to the Raanaa Bhojaraja of the Sisodia dynasty in Mewar. But Raanaa Bhojaraja was very supportive and used to support Her with Her Krishna Bhakti. He never came in between Her and Her Krishna Bhakti and enjoyed Her keertanas. Throughout Her life, She considered Herself as Krishna’s wife only.
But the other family members, especially Raanaa Vikramaaditya Singh (brother of Raanaa Bhojaraja), after the death of Raanaa Bhojaraja in the battle against the Mughals, tortured Meerabai a lot and even tried to poison Her. But nothing affected Her. She finally went to Vrindavan and stayed there. After that, She came to Dwaraka. And at the end, at Dwaraka, She merged inside the idol of Krishna. She Herself didn’t become Krishna, but She attained Krishna and went to His eternal Vaikuntha Dhaama.
Another story is in Her life history. It so happened that, before Her marriage to Raanaa Bhojaraja, in Her dream itself, Krishna appeared and married Her, as per Her wish. After that, She was physically married to Raanaa Bhojaraja, but was actually married to Krishna only.
[SriGirdhar Gopal (SriKrishna Paramatma) with Srimati Radharaniji (on left side of Krishna) and Meerabai (on right side of Krishna), worshipped by SriMeerabai, currently in Vrindavan]
Hope this helps!
Jay SriRam!
ShriGiridhar Gopala Abhinna ShriKrishnarpanamastu!