Jason in my years on this forum I've seen many versions of your story and they are all heartbreaking. It's not unusual for As in rehab to form intense emotional attachments, usually to other patients. Along with giving up alcohol, they are seeing the world unfiltered and adapting to it.
I know it seems heartless to say, but you have a decision to hang onto something that has finished, or work very hard on moving on. It's not easy, I've done it myself, but it will get easier as time goes by. You may feel that you haven't had closure, in which case you could see her personally write her a heartfelt letter and not send it.
Please consider blocking her and her family on social media. Give it a chance because clinging on hearing news of her and around her is only going to make things much more painful.
In your case, while I've no doubt she loved you, you were in another state, and she was presumably seeing this man day after day, all the time going through major changes in her life. She may have come across as dishonest, but possibly she was only becoming aware of her feelings gradually.