It's really really hard to control for confounds in studies like this. Some latent variable can decrease both life expectancies, husband and wife. E.g., black mold in the house, or poor eating habits, poor exercise, even common genetic factors if people tend to marry others who are genetically similar. Carbon monoxide issues from the heating system or in the car. Similar attitudes toward risky behaviour. Common sources of stress. Similar sleep habits. You can spitball this stuff all day, but unless you do a controlled study (which would seem unethical in this case) you're still going to have a lot of doubt about causality.