One such word is azygophrenia. It is defined as: the psychoneurosis of everyday unmarried life.
I did a little digging. Azygo comes up in the medical dictionary, but somehow I don’t think the Azygos Vein that runs up the right side of the thoracic vertebral column is related to marriage or neurosis.
The etymology of the word is as follows: Zyg is a Greek root meaning pair. A (in the Greek) means “NOT” so azygos mean unpaired.
Phrenia is a mental disorder. Schizophrenia being the one we are likely to all have heard something about.
One website sites an old study of personality disorders thusly:
zygophrenia: personality disorder, opposite to schizophrenia, as in the case of the Chaplin twins of York, England, described by Dr. David Westbury as one person in two bodies, evidenced to a lesser degree in the telepathy-like twin effect
The Aldritch Dictionary of Phobias and Other Word Families does in fact give the definition of zygophrenia as the “psychoneurosis of everyday married life.”
These words imply that marriage is like being conjoined twins, with all of the bother of knowing what the other is thinking, and having to deal with the other’s constant effect on a shared body. No wonder the divorce rate is high.