Is divorce predestined by Allah or a result of causes brought about by one of the parties?

Nothing occurs in the universe except by Allah's decree and will. Your divorce is by Allah's divine decree and destiny. Its direct cause may be from both of you or from one of you, as in His (the Most High) saying: "No disaster strikes upon the earth or among yourselves except that it has been in a register before We create it." And all the affairs of a believer are good: if he is afflicted with prosperity, he thanks (Allah) and it is good for him; and if he is afflicted with adversity, he perseveres and it is good for him. So be patient and seek your reward from Allah, and ask Him to compensate you with something better. For the Messenger of Allah (peace be upon him) said: "There is no Muslim who is afflicted by a calamity and says what Allah has commanded: 'Indeed we belong to Allah, and indeed to Him we will return. O Allah, reward me in my calamity and replace it with something better than it,' except that Allah will replace it with something better than it."