There are clear, and published reports that at least "married" life is healthier than single life. I can not recall in detail to provide you with references, but they do exist.
What I do remember is that, married people, have healtier habits, diet, live longer, lower co-morbidity rate, and in general make up the lowest % of various "risky behavior/life style" lists. This even goes to include psychiatric and mental health.
I do not recall if the researchers made a point about being "monogomous" in the relationship, but one can assume that married people are "more" monogomous during a given, arbitrarily chosen, period than a single individual. Lets say over a 12 month period, a single person can practice "serial monogomy" and by the end of the year having been with 52 people (one for each weekend), and yet have escaped the definition of "polygamous" since he never "cheated" on his week long partners, he just changed them "serially". On the other hand, a married person, even if tried, could not reach that number in 52 weeks. Therefore, married life, fundamentally, reduces risky behavior, and therefore, reduces the incidence and prevelence of various diseases to begin with. In addition, from a psychological stand point, people who feel and receive love, are healthier, and that has been proved as well. Even post-op patients who are recepient of love and affection have a better prognosis and sooner recovery. I could go on and on about this, but have to leave now.
Enjoy.