This phenomenon is mentioned here in WebMD:
Frank Sommers, MD, a Toronto psychiatrist, worries that excessive vibrator use during masturbation could desensitize women to orgasms with a partner. “I tell my patients, ‘Look on a vibrator as whipped cream—you wouldn’t want to eat it every day.’’’
He believes too much vibrator use ‘’habituates your autonomic nervous system to such stimulation that a human could not duplicate it.”
Do you use any dopamine agonists such as pramipexole ? This paper says they are associated with hypersexual activities such as a lot of masturbation. You may also have elevated levels of testosterone.
One answer to a question about the side effects of masturbation said that you have to do what you’re trying to do: throw away the vibrator.
I agree with @whatthefluther: do it the way you’ve been trying to: cold turkey. It’ll be a real pain at first, but if you can stick it out, you’ll be free. However, if what that last website said is true—it’ll still take a while before you can achieve orgasm through oral.