vs
QUICK ANSWER
"Obsesionado" is a form of "obsesionado", an adjective which is often translated as "obsessed". "Preposición" is a noun which is often translated as "preposition". Learn more about the difference between "preposición" and "obsesionado" below.
la preposición(
preh
-
poh
-
see
-
syohn
)A feminine noun is almost always used with feminine articles and adjectives (e.g., la mujer bonita, la luna llena).
1. (grammar)
a. preposition 
En la frase "estoy loco por ti" la preposición es la palabra "por".In the phrase "I am crazy for you," the preposition is the word "for".