Double Life Sam is used to having affairs with women on his report trips and thus he is deceiving his wife. But Anna is something different for him.
They both know that the time spent together is limited and that they are going to return to their common lives. What they experience is special exactly because it is forbidden, precious, limited...
Anna suggests spending one weekend a year together in a hotel in London. They both get back home, they hope to meet sometime in the future.