I would venture to guess that there is a certain amount of fusion in every relationship...it's the nature of the beast. The problem arises when the self gets too sacrificed for the sake of the relationship. Objectively, I see this in pretty much every case here on the board, but each of us has to figure out this line for ourselves.
IMO, you will experience fusion again as your relationships mature, but NEVER in the way that you did in the past. And that's growth.