I don't agree with the above responses. You don't know how happy she is with her partner. She might be looking to leave that relationship. She might long for you too. I recommend you find quiet circumstances (away from inquisitive eyes and ears) in which to ask her out, and see what she says. Even if she says no, at least you then know where you stand and you can stop wasting your thoughts on her. If you say nothing, you might meet up again many years from now and, on admitting you once had a thing for her, she could say "I wish you'd told me at the time...I was in a really unhappy relationship....I really fancied you but had no idea you were interested....but now I'm married with kids." No time like the present. Go ask her....and please let us know how you get on.