Kirsty, you stop being angry by realising that her being your partner and carer was too much to ask of her. The situation she was placed in would have been intolerable for the best of people.
To go on a tangent, I'm now wondering if she knew she knew that you considered her a girlfriend. The fact that she has a new love interest and still wants to be your friend makes me think she only ever saw herself as carer with benefits to you. I suspect that you saw this as a much more serious thing than she did.
At this point, I suggest that the best way to move forward is to move out and end the friendship. As much as the situation may have been intolerable for her, she's crazy if she thinks she can move on with someone else and still be your friend.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.