Its pretty unlikely that one of you won't feel a desire to pursue a more formal relationship from what you've said. I think you should wait for the opportune moment, act, and see what happens.
However, no matter how much I want to give you advice on what to do, you have so much better information than I do. I hope stuff works out one way or the other, but either way that you both benefit from your friendship/whatever.
Good luck ... you're gonna need it.