You are correct. So many people live in homes with others but are more lonely than those who are single. Often, the individual with whom they live is completely oblivious to the fact their partner is unhappy. Of course this is one of the main reasons they are so terribly unhappy.
I know this to be true because I was one of them. At least until 7 months ago when I finally left a miserable 38 year marriage. My husband's first words when I told him I was so unhappy I could no longer stay in the marriage were, " I'm stunned." Yet he didn't ask me to stay and there were no tears.
It's entirely possible to live in a house with a partner and feel as though you are the loneliest person in the world.