PHOENIX - An Arizona sheriff resigned as co-chair of Republican presidential hopeful Mitt Romney's campaign in the state on Saturday after he was accused of threatening a former male lover with deportation to Mexico if he talked about their relationship.In an embarrassing incident for Romney's campaign, Pinal County Sheriff Paul Babeu denied he or his lawyer made the deportation threat, but he stepped down from helping the former Massachusetts governor in the border state.Babeu acknowledged at a news conference on Saturday that he is gay and had a personal relationship with the man making the allegations, whom he identified only as "Jose.""Sheriff Babeu has stepped down from his volunteer position with the campaign so he can focus on the allegations against him. We support his decision," the Romney campaign said in a statement.The sheriff, who is a tough law-and-order advocate, was considered a rising star in state Republican politics and a strong candidate to win the Republican nomination for a congressional seat in Arizona this year.The Phoenix New Times alternative newspaper reported this week that Babeu's lawyer had asked Jose to sign a legal agreement that would require him to keep quiet about his involvement with the sheriff . According to the newspaper, the lawyer also warned Jose that any talk about their relationship could imperil his immigration status."All of these allegations that were in one of these newspapers were absolutely false, except for the issue that referred to me as being gay, and that is the truth. I am gay," Babeu told the news conference.Babeu first came to statewide prominence in 2010 when he appeared in a campaign ad for US Senator John McCain of Arizona, the Republican presidential nominee two years earlier, calling for tough immigration measures.Babeu is a strong critic of the handling of immigration issues by US President Barack Obama's administration. Republicans are seeking a nominee to challenge Obama in November's election.