The roommates parents may be rude or ungrateful or whatever.
But that’s a simple fix- tell the roommate you can’t drive him any more- problem solved. No more resenting another family when you aren’t in the middle of it. Whether the kid gets home every weekend or not is no longer your problem since he’s not in your car.
So to me- that’s a red herring- easy fix. The underlying issue- that every single weekend is being spent behind the wheel- is the harder problem. How to deal with the mixed emotions- happy to be helping your kid, thinking about what you could be doing with an extra 12 hours in your life every single weekend-- that’s the rub.
But in the same way that you don’t get to tell the other parents what they should or should not be doing, adults need to learn to own their own decisions. You CHOOSE to drive your college aged kid 12 hours every weekend? That’s your choice. And if the OP would feel better about that choice if she didn’t have the roommate tagging along? Tell the kid to find another way home. Problem solved.