So the "forget everything at the town line" is the price of magic. What Rumple wants the most, he can't have.
Yep. Rumple told Regina that magic was unpredictable in Storybrooke, but he also clearly wasn't expecting it to be THAT unpredictable. He brought magic to Storybrooke to give himself an advantage, most likely over Regina given their long and complicated history and rivalry, but, as was the case when he became the Dark One in the first place, he ended up inadvertently screwing himself over, since introducing magic created a 'secondary curse' that has trapped him - and everyone else - in Storybrooke as effectively as the original Dark Curse did, but with greater detrimental effect.