Mr Milingo's marriage caused problems for the Church
Archbishop Emmanuel Milingo, 71, married South Korean doctor Maria Sung in May in a mass wedding typical of the religious movement known as the Moonies.
But after a personal meeting with Pope John Paul II, Mr Milingo is reported to be "renouncing my living together with Maria Sung and my relationship with the Rev Moon", according to a letter released by the Vatican.
Ms Sung, 43, told reporters on Monday she might be pregnant by the prelate.
Ready to die
Ms Sung said she began fasting at midnight on Tuesday and vowed to die if Archbishop Milingo renounced their marriage.
The Vatican threatened to excommunicate Archbishop Milingo after news of his marriage became public.
Speaking to reporters outside Saint Peter's Basilica in Rome, Ms Sung told reporters: "If he [Archbishop Milingo] decides that this is no longer real then I'm ready to die. As a spirit, I will be near him."
Italian media reported Ms Sung said she was not aware before the wedding ceremony that Catholic bishops were not allowed to marry.
No sightings
Archbishop Milingo, originally from Zambia, has not been seen in public since the couple held face-to-face talks with the pope at his Castelgandolfo summer residence.
The Vatican has not disclosed Archbishop Milingo's whereabouts, other than to say he "had decided to pass a period of reflection and prayer ahead of his full reconciliation" with the Catholic Church.
Mrs Milingo has said she will not take a pregnancy test until she is reunited with the archbishop.
She said she was worried that the results would be used against her no matter what they were.
"If it comes out positive, people will say I am using it to get him back and if it is negative, there is a risk they will just let me go."
Mrs Milingo said the risk her hunger strike posed to any unborn child was "secondary" to her concern for her husband.
She said she planned to pray for the archbishop at the Basilica every morning to ask for him to be returned to her.
Vatican officials have said little publicly about the affair amid fears the case could lead to a breakaway movement of followers loyal to the charismatic archbishop, who they have struggled to control for decades.