Helio
I can certainly sympathize with you regarding conflicting  B-12 information. I
have a pretty good supply of information from recognized B-12 authorities which
contridicts each other.Some do say the body is able to store large quantities of
this necessary nutrient. I,personally do not take a chance, and take B-12 in
sublingual form about 4 times a week when I am not consuming B-12 containing
foods.  If this  issue is important enough to you, consider having a blood test
done. You would then have a definitive answer.
    Regarding the larger question of diet/mental functioning: does your diet
include adequate quanities of essential fatty acids? Could you be suffering from
low blood sugar with your 70% fruitarian diet? If you wish to post more
information about your diet, I will try to be more specific.
Best of luck
Roy Siegel