The answer is "they can."
The "it depends" part applies to pretty much everything ever. I met my wife while around the time I broke up with one girl and started going out with another. The new girl and I actually moved in with my now-wife and, almost a year later, broke up. Over that time, my now-wife and I developed a good friendship (completely platonic, at the time). I dated my wife for 2.5 years before we were married and it's been 15 months since then. We both agree that our friendship was and is the foundation of our relationship.
Though, to be fair, most of my ex-girlfriends were my friends first, as well. So it's not like it's a sure thing (nothing ever is).
So, while the answer is "they can," my answer is "good luck."
And try to have fun, along the way.
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Waltur the Walrus Slayer,
Militant Asantist.
"BLASPHEMER!! !! !! !!" (according to AngelRho)