Rumple clearly thinks of himself a coward at times. But I've always felt it was more... emotional cowardice, if that's a word. Like not daring to believe Belle would love him in 1x12 and stuff like that. Not daring to follow Bae into the bean portal.
His addiction to power/magic can also be partly motivated by fear, which might be why Rumple considers himself a coward.
Might be that remembering Neal and what Neal did will help Rumple in the long run. I sure hope so.