Many happily married couples, young and old, sleep in separate beds or even separate bedrooms. Somehow, this real life situation has for long escaped public knowledge, but has been practiced forever. The image presented in contrast is that a couple that does not share the bed is somehow not happy to be together.
There are many reasons that couples choose to sleep separately. Some of them are issues that are health related but remain taboo for open discussion simply becasue the couple feels their relationship will come under scrutiny. That attitude can only change if the practice is openly discussed.
The commonest reason I hear is: "he/she snores so loudly it wakes me up".
Snoring is an "alarm". It is telling you the person snoring is not able to breathe well in sleep, which represents sleep apnea, a major health problem. If you can not "hear" the alarm generated by your loved one's body, you really should doubt how much you care for them. Unfortunately, we all are guilty of this crime of ignoring alarms, because they are going off all around us, and are so common they become a subject of jokes, rather than being addressed as a health problem.
The next common one is: "I need to go to work in the morning, and he/she stays awake at night disrupting my sleep." This statement could be applied to mothers nursing babies at night, "night owls", creative people playing music or writing at night, or simply insomniacs.
Sleep is the keystone of health. Its the glue that holds the body together. If an individual has a sleep problem it is the responsibility of their friends, well wishers, loved ones, spouse and partner to get help for them and remind them of how it may be affecting their life. Unless of course, the sleep issue is situational and temporary, related to a known reason, such as a work project, school tests, or a temporary medical condition, for example painful problems, asthma, etc.
Those of us who are lucky to have someone sharing our life, should also be lucky enough that these people watch out for us when we are unable to, such as often occurs with sleep problems. Sleeping in a separate bed or separate room is just a practical solution and there is nothing really wrong with it, except that it most often represents not just a major mismatch in the partner's lifestyle, it often results from ignoring a real health problem that requires attention. Think about it.