I (M23) kissed my best friend (F23) and we don't know where to go from here... Last night I kissed my best friend of 8 years and she kissed me back. We're really close. 

But we can't decide whether it's worth the risk to have a physical relationship. 
First off, I've just moved so we're further away than we used to be.
Second, I'm friends with her ex and so is she and he could take it pretty badly.
And if it does go wrong, which it might, we might not be friends anymore...

Any thoughts?

Tl;dr Kissed best friend, not sure whether getting together is a good idea, particularly because of mutual friend-her ex.