I'm concerned about one of my roommate's cat
What concerns you about the cat?
I just want to help the cat.
I assume your roommate is helping the cat because it is theirs. It is nice for you to want to help out with that.
The cat never eats and it is starving. I tried to give it food, but it really doesn't want to eat. It's sad to see the cat like that.
If the cat won't eat, tell your roommate to take it to the vet. All pets need food to eat, something may be wrong that you cannot diagnose on your own.