I'm just speculating, but if you flew to Boston first on your previous cruises, then I'm guessing you flew on United, as Boston I think is one of their major cities. As Cruise Fanatic states, for this upcoming cruise you're most likely on either Delta or Northwest.
2007 - Majesty of the Seas (Bahamas)
2009 - Enchantment of the Seas (Western Caribbean)
2010 - Freedom of the Seas (Western Caribbean)
2013 - Golden Princess (Alaska, roundtrip from Seattle)