FOR Colette Hayward and Margaret Selby, the problem is this: Maryland recognizes their 2009 marriage, but the federal government does not. The ramifications are maddeningly complex, no more so than when they deal with the Internal Revenue Service. Two years after taking legal action to assert their rights as a married couple, they are paying a price when they pay their taxes. For Ms. Hayward, 47, a lawyer who owns two construction businesses, and Ms. Selby, 48, a Baltimore County police officer, a big issue involves insurance benefits they fought to achieve. They are paying taxes on those benefits, even though such benefits for spouses normally are not taxed. For same-sex couples across the United States, an offshoot of being married is a dizzying set of complications in computing taxes. Although nine states and the District of Columbia have approved same-sex marriages — two others recognize marriages conducted elsewhere — the federal 1996 Defense of Marriage Act prohibits such unions from being recognized by the federal government.