Simple, I'd wait until the time is right - then hint around about "us" being a couple. If the first hints, didn't get through, I would jokingly (at the perfect time of course) make a wild statement and wait for a reaction. Testing the waters to see where his / her affections lie is the best way to sum up if a future together is possible. Many many people fall in love with their best friends. Some like my friend Lisa ended up marrying him. Love has no boundaries, knows no bias, is always truest.