When Athens Family Restaurant got forced out of its longtime Melrose location, it looked like the much-loved Greek diner was a goner. But local restaurateurs Arnold and Anna Myint came to the rescue, offering their Belmont restaurant PM as a site for Athens to stage a daily daytime pop-up, with PM operating at night. Before long the relocation became a permanent thing, as the Myints decided to close PM and allow Athens to occupy the space exclusively. (The Myint siblings are concentrating on their revived incarnation of International Market, their late mother Patti’s foundational Thai restaurant.) Athens has spread its wings in the new space on Belmont Boulevard, and the food seems even better than before.