It can lead to a lot of emotional turmoil. The wife may feel angry, sad, and humiliated. The husband, on the other hand, may end up feeling guilty if he realizes the wrongfulness of his actions. In many stories, this kind of spying also affects the family environment, causing stress and tension among family members.
In the long run, it can completely destroy the relationship. The wife may lose respect for her husband. Also, it can have a negative impact on their social life. Friends and family may take sides, and the couple may become isolated. Moreover, if the spying involves illegal methods like hacking into her accounts, there could be legal consequences for the husband as well.