The BBC is reporting on a study by Gwen Sprehn and colleagues at Indiana University on the effect of marital status on surviving cancer. They found, as other research has, that married people are more likely to survive than unmarried people. The new element in this study is that those who are separating are the worst off.
The usual understanding of why married people live longer is that they have someone to care for them and to live for. I think what this research adds is that separating is positively harmful to your health. You don't just lose the benefit of marriage, you add a killing stress.
Married - 63% survival after five years and 58% at 10-year mark
Never-married - 57% and 52%
Divorced - 52% and 46%
Widowed - 47% and 41%
Separated - 45% and 37%