Sorry, you are out of luck.
And yes, you may act like nothing happened.

I guess you can combine two previous advices: keep a distance and have fun.
i.e. keep in mind she's totally flaky, you dont want that flaky person around in a long term.

if she is that flaky, treat her as a flaky person.

But there is no reason not to be friends with her and have fun
(means you as well can just forget about your agreement, can drink with her, touch her, but still keep in mind you dont want to be with her - just imagine she'leave tomorrow anyway)