What is the ruling on one who has vowed to Allah thousands of times to abandon masturbation, then returned to it? Is this considered hypocrisy? And is there a fear that he may be deprived of repentance?

Masturbation is forbidden and has its harms. Previous fatwas regarding its prohibition and methods of abstaining from it can be consulted. There is a significant difference between permissible intercourse and masturbation. If you make a covenant with Allah to abandon a bad deed and then break that covenant, repeat your repentance and do not despair of Allah's mercy. It is recommended to trust in Allah, supplicate to Him, take measures to reduce lust, and hasten to marry.