I am very new to the poly scene but I can tell you this much; You don't have to move out. Nor does she have to move in.
All that really has to happen is very open and direct comunication about expectations and intent.
What does she expect in a relationship with you? What do you expect in a relationship with her? Make sure that is all out on the table.
Then make a game plan as it were; "This is how this relationship works."
Just because you live in one building or with one person versus another does not negate your love for the other person.
Just make certain that everyone knows all the expectations emotionally and physically so that no one gets hurt later. (Or at least, no one can say they didn't have fair warning.)
With all my heart I will love and not fail,
With all my soul I will fly and not fall.