Should personal account breaches be ignored, relying solely on future precautions, or should one continue changing accounts?

You did well by ceasing communication with this young man and cutting off conversations, as it opens a door to evil, and it is a sound path for self-purification. As for the young man hacking your account in an attempt to access your secrets, it is a reprehensible act and an act of spying that the Sharia has forbidden. You can threaten him with reporting the matter to the responsible authorities. You are free to continue keeping your account open while taking the necessary measures to prevent others from accessing it, and avoid publishing anything you do not wish others to see.