Sleeping separately isn't always a sign of a rough marriage.
Some people have different mattress needs (like one might need it firm, the other might need it soft). Additionally, if he has to leave really early for work then he might not want to wake her up, which is why quite a few couples do sleep separately (especially if there are schedule differences, like if one works the night shift and the other the day shift).
And heck, if they're young and short on money, they might just figure it'd be cheaper to keep their current single beds from when they lived alone instead of buying a brand new king-sized bed.
Sleeping in different beds doesn't indicate strife. A true sign of a content marriage is ditching the insecurity of what others may think, and doing whatever is comfortable for the two spouses.