Okay I just rewatched the scene a few times.
Rumple speaks to Belle-box about her dreams and then the room starts to shake. Rumple actually acknowledges what is happening: “a portal” he says.
He then looks at the Belle-box, the crystal and back again at least twice if not three times. In other words, he had enough time to pick up the box and get to the crystal before the actual portal opens on the bed. He then lunges for the crystal and then looks back over to the bed where the portal opens.
I think he made a deliberate decision in that moment (however he will rationalize it, he went for the crystal first after thinking about it)
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"He was a lot of things to me" "The only conclusion was love"