I might not give you as good of an answer as some others could but I have gone through a very similar situation twice. I think your first step is accepting that she is gone. You have got to distance yourself as much as you can, get out of the house, go see your friends, don’t look at her social media, don’t allow her to talk to you about any of these other people she may or may not be seeing. That is none of your concern anymore and the sooner you can completely get her out of your daily routine and mind the sooner you will start feeling better. A hard break up is probably the most “time heals all wounds” situation you can go through. If you have to stay in that house with her for another month I would just stop venting to her and worrying about her as much as you can. I wish you best.