Forum:How far can I go with Miranda before I lose Ashley?

Hey, I'm playing through Mass Effect 2 and need soem help. I imported my save of ME1, in which I had a relationship with Ashley. I heard if you persue a relationship with Miranda, the picture Shepard keeps of Ashley on his desk will be face down, ending the relationship. My question is, how far can you go with Miranda before the picture goes down? Can you flirt with her and just end it before the relationship gets physical, or of you flirt too much even without spending the night with Miranda, will Ashley's picture go down?