De or het roommate?

The correct Dutch article is:

de roommate

Rule Words ending in -te: usually de. See the rule

How to use roommate

the roommatede roommate
this roommatedeze roommate
that roommatedie roommate
our roommateonze roommate
your roommatejouw roommate
every roommateelke roommate
which roommate?welke roommate?
a big roommate / the big roommateeen grote roommate, de grote roommate