Yes, your heart is completely in the right place, but you need to go into this school year getting along with your roomates! If you go against their wishes and get the pup anyway, you will be completely starting off on the wrong foot.
I would make it clear to them that if they disagree with you getting another pup, then they cannot get any more pets either.
Mikey, you have assisted in the adoption of so many pets now. If you look around you, you will probably be able to find another one of your friends who would be willing to take the Westie. Good luck, honey!