Is it valid to atone for the sin of spying on a female relative and alienating her husband against her, and attempting to expose her, followed by regret and an attempt at reconciliation? And is it a condition to confess the sin to the husband for repentance to be valid?

Repentance is achieved by abandoning the sin, regretting it, and resolving not to return to it. If the sin involves a right due to another human being, then it is a condition to return that right or seek forgiveness from its owner, based on the saying of the Prophet, peace and blessings be upon him: "Whoever has wronged his brother concerning his honor or anything else, let him seek his forgiveness today."

Therefore, it is obligatory to seek forgiveness from the female relative and her husband for the injustice done to them. It is sufficient to generally ask for their pardon without exposing oneself. However, if a great harm is feared from seeking their forgiveness, then repentance to Allah and seeking His forgiveness suffice.