You know... in the regular world, lots of people get together and have fine relationships until the get married, divorced, and eventually come to realize they were better off as friends, both before and after the marriage.

So why mess with it. If it works as is, I say go wherever it takes you. Let it, the relationship, guide you instead of you trying to guide it. You might find it takes you exactly to the place you wanted to be... or you might find it takes you somewhere else you never considered, be it for better or worse.

My take is, it will be a better place for having grown there naturally rather than because of some predetermined expectation set into your psyches associated with the vanilla upbringing most all of us are saddled with.