The GSE executive exodus continued last week with the announcement that the executive who oversees Freddie Mac’s single-family mortgage business has resigned. Anthony Renzi, Freddie’s executive vice president of single-family business, operations and information technology, will leave the company effective May 11, according to a filing with the Securities and Exchange Commission. Renzi, who came to Freddie after being forced out of GMAC Mortgage in April 2010, will join Citigroup Inc. as its new chief operating officer. The company said Paul Mullings, senior vice president of single-family sourcing and securitization, will take over Renzi’s duties on an interim basis.