The apartment means the life they built and all the memories they have.
We can arrive at this answer because:
Shay and her family are leaving the house they've lived in all their lives as they move out of town.
This change will be accomplished because Shay needs to follow her dreams and it's not possible to do that in the city where they've always lived.
While it's nice that Shay can fulfill her dreams, it's sad to have to leave a home with so many memories and where Shay and his family have built their entire lives.
They have a very strong emotional attachment to the house, but it is necessary to say goodbye to it.
