I think you are only looking at it from your perspective. Turn it around.
She thought you were in a relationship, she loves you and believed that you loved her. She is now going through a break up. Being friends after a breakup is incredibly difficult and usually requires a long period of space before it's possible. She has the right to not want to be friends.
But you aren't asking to be friends. You are asking her to be your friend, your confidant, your lover, your partner in all but name, while allowing you to see other girls. Do you see how this situation suits you, not her? You can't have it all ways.
And if you are asking to genuinely just be friends, you need to recognise that it would be painful for her, and that's not fair.