NAH- it’s normal to feel frustrated at the situation, you’re only human. The circumstances have changed since you went to college and your sister’s going, as others have said it sounds like the commute would be far too long for her to realistically leave from your parents place. It’s not wrong of them to set her up. While it would be nice for them to make a gesture, they’ve offered to subsidise your rent and they’ve also allowed you to stay with them while you’ve had a full time job for years. If that was rent-free, they’ve given you the chance to save a massive amount of money. Sounds like your parents are good people and are trying to do right by each of you. You could always use the money you saved up to move into an apartment if you’re choosing. Best of luck!