The teen's future flatmates can expect to see the pair snoozing together at night, sharing pizza and watching cartoons together - Billy loves Adventure Time.
Mess wise, there's some toilet training to do, as Bailey's university course may not allow her to be with her furry friend 24/7.
"Hopefully the lecturers will be nice enough to let me have her in lectures."
Bailey said she wanted people to give possums a chance.
"It's not their fault they're the way they are. It's just about being considerate, she's not doing any harm with me, so don't put a label on her.
Auckland Council said there were no laws that prevented people from having possums as pets, but it did undertake possum control across the Auckland region as they compete with native animals for limited food resources.