File this under the "duh!" category: research suggests relationship issues reduce the quality of sleep, and poor quality of sleep reduces relationship issues. This is an example of the famous "sleep fights" made famous in my circles by a couple that, er, wasn't immune to relationship issues.
The other remark is that married women seem to have better-quality sleep than those who are never married, widowed, etc. You would think the latter comparison would be best made between currently married women and widows several years after the widowing, with the hope that ideally the widowing death would have been basically random and not long-lasting in its inducing of insomnia. Maybe never-married people don't get married because they can't sleep!