A same-sex marriage advocate is finishing a cross-country bicycle trip in Portland that’s raised money for gay marriage initiatives in Maine and other states. Richard Carey of New York City began his 3,700-mile, 54-day trek in June in Vancouver, Wash., to raise money and support for the legalization of gay marriage. The 53-year-old Carey ends his trip Tuesday in Portland, where he’ll join gay-marriage supporters for a press conference at the headquarters of the Mainers United for Marriage organization. Carey has raised about $16,000 during the trip that will be used in support of gay marriage efforts in Maine and other states. His goal is to raise more than $25,000 in all. Mainers will vote in November on a referendum seeking to legalize same-sex marriage in Maine.