How can one cope with the death of a husband and the depression resulting from his loss, and how can a woman be forgiven by her deceased husband for taking money without his knowledge?

May Allah عز وجل improve your solace regarding your husband. Among what aids you in patiently enduring his departure is your knowledge of what Allah has prepared for the patient. Allah Almighty says: "Indeed, the patient will be given their reward without account." If your husband was withholding your right to maintenance, there is no blame upon you if you took from his money the equivalent of your maintenance in a reasonable manner, without his knowledge. However, if he was providing you with your obligatory maintenance, then you are mistaken, and you must repent and feel remorse. Part of the completeness of your repentance is to return the amount you took to his estate.