Rumple doesn’t ask Charming to help Belle to get her memory back, he ask Charming how he and Mary Margaret could have fall again for each other while cursed.
I think the help is not helping Belle, but helping Rumple figure out how to win back his true love even though she no longer knows who she is and has a totally different identity.
*is it the 21st yet?*
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"He was a lot of things to me" "The only conclusion was love"