In Pathfinder and 3.5e D&D, are Blindness/Deafness separate spells, by which I mean do you need to learn each spell individually to cast them or does learning one mean you can cast the other?
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No.
Unlike detect evil, et alia; magic circle against evil, et alia; and protection from evil, et alia; blindness/deafness is a singular spell which asks the caster to make a choice when casting as to which effect will attempt to manifest.
Blindness/Deafness (PH, p. 206)
[...]
You call upon the powers of unlife to render the subject blinded or deafened, as you choose.
Contrast this language and spell entry with detect, protection and magic circle spells, which not only have separate entries, but do not offer any option to choose to the caster. Magic circle against chaos is only ever protective against those creatures and effects spelled out in the description.
Finally, examining the entry for remove blindness/deafness (PH, p. 270) makes it clear that blindness/deafness is a singular spell, as the counterspell entry in remove blindness/deafness refers to blindness/deafness as a singular spell.
