Does divorce occur by means of obsessive thoughts, imagination, and repeating its phrases to oneself, with the strong presumption that they were not uttered aloud?

What has been mentioned are merely intrusive thoughts (waswas) that do not result in divorce at all. Therefore, you must completely disregard them in every detail, for yielding to intrusive thoughts has dire consequences. Among the things that help in getting rid of them are: seeking Allah's help, sincerely turning to Him, and supplicating frequently.