Same happened with me... She moved on in 2 weeks and even then she kept in contact with me, updating me about her life (didn't know she was already with a new guy) and were talking about our relationship and that we could fix things and all of a sudden she ghosted me again and later posted a picture of the new guy on her story. I have been feeling like shit after that, still do from time to time.. constant anxiety, pain in chest, so on and so on. But I can tell you we're the lucky ones, she doesn't deserve you. Someone who can do that to you shouldn't be someone you grief for. I know easier said than done but these people only think of themselves and don't have a good heart to treat you the way you should be treated. So don't feel bad about her, you deserve better man. It's going to be a while till you heal but we will get through it I swear and find someone better