Is it permissible to leave Medina due to longing for family and psychological pressure, along with the fear of disobeying the Prophet's (peace be upon him) command to endure its hardships and difficulties?

You are not at fault for terminating your contract for the reasons mentioned. This does not fall under impatience with the hardships and difficulties of Madinah, for your departure is not due to distress from its adversities, but rather out of righteousness towards your mother and to preserve your chastity.

The more preferable and complete approach is to combine both matters: bring your wife, and visit your mother frequently, so that you may attain the virtue of residing in Madinah and fulfill the great promise of receiving his (peace be upon him) intercession.