A gay veterans group said Wednesday it has been denied permission to march in this year’s Boston St. Patrick’s Day parade just two years after organizers made the groundbreaking decision to allow gay groups to participate for the first time. OutVets, which marched in Boston’s 2015 St. Patrick’s Day parade after decades of resistance from organizers, said on its Facebook page that the reason for the denial to this year’s parade is unclear, but “one can only assume it’s because we are LGBTQ.”