Meloni told reporters last month she should not be judged over Giambruno's remarks and in future would not answer questions about his behaviour.
The split comes as the 46-year-old prime minister celebrates her first year in office at the head of a right-wing coalition government that has defended the traditional family as one of its policy hallmarks.
"My relationship with Andrea Giambruno, which lasted almost 10 years, ends here," Meloni wrote on her social media accounts on Friday.
"Our paths have diverged for some time, and the time has come to acknowledge it."
Meloni said she would not be distracted by difficulties in her private life, saying, "all those who hoped to weaken me by striking me at home" would have no success.
The couple, who met in a TV studio in 2014, have a seven-year-old daughter.
Giambruno, 42, is the presenter of a news program transmitted by Mediaset, part of the MFE media group owned by the heirs of the late Silvio Berlusconi, a former prime minister and Meloni ally.
This week, another Mediaset satirical current affairs TV show broadcast off-air video excerpts from Giambruno's program showing him using foul language, touching his groin and appearing to make advances to a female colleague.
"Why didn't I meet you before?", he asks her.
In a second audio recording aired on Thursday, Giambruno is heard talking about being in an affair and telling female colleagues they can work with him if they take part in group sex.
The TV journalist had been widely criticised in August for comments interpreted by many as victim-blaming, following a gang rape case.
Giambruno was not immediately available for comment.
Marco Furfaro of the opposition Democratic Party said Giambruno's comments were "pure chauvinism and sexism.... uncommentable filth."
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