My wife is my soulmate, and I love her more than life itself, but honestly the only reason we actually got married was to promise ourselves to be faithful to each other. We didn't need the big expensive ceremony (we got married in Vegas, just the two of us), we aren't going to have children, we lived together for years before making it official. We could have promised ourselves to each other without the legal papers and lived happily ever after, but marriage just makes it easier to explain it to family and friends. Our lives are no different after being married than it was before, it's just official now.
I think marriage is important for couples having children, but if two people just want to spend the rest of their lives together and they trust one another, then I don't feel it's as important. I know two couples who have lived their whole lives together but never got married, I don't see their love for each other being any less strong than my wife's and mine's.