Two New England states have already legalized same-sex marriage, and a Boston-based advocacy group wants to see the other four join them. Gay and Lesbian Advocates and Defenders, known as GLAD, has launched a first-of-its-kind regional campaign aimed at winning approval for same-sex marriage in the six-state New England region by 2012. Same-sex marriage is already legal in Connecticut and Massachusetts, a result of court decisions in cases brought by GLAD lawyers. The 2003 Massachusetts decision was the first in the nation, while the Connecticut ruling went into effect Nov. 12. "We can make New England a marriage-equality zone ...