We've lost count of how many times these two have been separated, either by choice, curse, or terrible luck. Belle's been held hostage in a mental hospital, Rumple's died, ventured to Neverland, and been kidnapped by the Wicked Witch. And that was just in the first three seasons!
Like Tinker Bell, we will take any excuse to have Ariel back on our screens. Belle was one of the first people she met in Storybrooke, and the two bonded when they took on kidnappers together. Considering everything that's going on right now, Belle could use a friend.