Because Rumple can see the future I have thought for a very long time now that all the deals we see him making prior to the long break over the winter were in order to ensure 1) that he remembers who he is in SB and 2) that he has a way to break the curse, or at least assist Emma in the breaking of the curse. He is very invested in SW because she has to have Emma and he is invested in MM because if the curse set off by the EQ is based initially around her hatred for SW, it follows that you are going to need MM to break it.
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"He was a lot of things to me" "The only conclusion was love"