In the Romance languages, prepositions combine with stressed pronominal forms that are distinct from the unstressed clitic pronouns used with verbs.
In Portuguese, Spanish, Italian, and Romanian, prepositions generally combine with pronouns that are identical in form to nominative (subject) pronouns, but there are unique prepositional forms for the 1st and 2nd person singular (and 3rd person reflexive).
This is also true in Catalan, but the 2nd person singular prepositional form is identical to the nominative.
Portuguese and Spanish also have unique forms for 1st, 2nd and 3rd person reflexive when they follow the preposition com/con ('with').
However, the 3rd person non-reflexive pronouns (which are vowel- or glide-initial) take the prefix n- when they are the object of a preposition.