Obviously with him on the west coast and you on the east, you're going to have asymmetrical flying times no matter where you choose. I would hesitate about SE Asia with only a week - too many hours (for both of you) in transit.
Two thoughts come to mind. First is the Yucatan. Visit Merida, Chichen Itza, Tulum... You could fly into Cancun (but I wouldn't stay there) but once you're away from the beachfront glitz, the country (and Merida itself) is fascinating and beautiful.
Second, Andalusia. Fly to Gibraltar or Malaga from London, get a car, and stay near Tarifa. There are white villages like Vejer de la Frontera or Medina Sidonia, Roman ruins, beautiful beaches, frequent ferries Morocco. The weather will be decent - not hot but not cold, the food good, and it's quite inexpensive in the off-season. If you want, Seville is only an hour or two away.
Some photos of the area from a trip we took in February a couple of years ago -
http://gardyloo.us/February%202012.htm Highly recommended.