I am very sorry to hear that this is happening to you.
Take it from someone who got the "I need space line" two months ago. It's over and there is nothing you can do to fix it.
You're not gonna want to hear this but you have to forget about anything you thought you two had together. Your past with this woman is irrelevant now. She has lost all interest in you and the remaining interest she has is dropping drastically every day. You have to forget all the times she looked you in the eyes and told you she loved you. The way she once felt about you and how she feels now are completely different
Let me ask you a question, would you tell a woman you loved and cared about that you need space from her?
please please please please take the dongorgons advice. Cut all contact with her right now. There is still a small chance you can save this if you cut all contact with her right now.
Don't make contact with her at all and ignore her for at least 2-3 months. If she is still calling after that amount of time and wants you back you can choose to take her back, but under your terms.
Also if you take her back make sure you make it clear to her not that her behavior is unacceptable and that by doing that she has lost exclusive rights to you and has to earn them back very slowly
Again there is about a 1% chance of getting her back because she most likely has someone else chosen now so don't get your hopes up.
Even if you can't get her back I promise you will feel so much better than if you chase her because it is only a matter of time until she delivers the final blow.
Trust me. I was in an almost identical situation to you two months ago, but instead of letting her go I got super clingy and tried to convince her how much she loved me. I made a thread on here and everyone told me the same thing "cut all contact and disappear", but I didn't listen. I told myself my situation was different and that she loved me. Now I am super depressed and can't stop thinking about her and I cry a lot because I can't control my emotions. I let her take my soul and self respect and now I have to build it all back up bit by bit.
Again I am sorry for this happening to you. A bad relationship is like cancer. If you stop it early enough you can heal it with only minor pain, however if you ignore it and do nothing then it will cripple you.
EDIT TO GET AROUND 10 POST LIMIT
Everything you said in the post below is irrelevant. She is already over you. Whenever a person pulls the "I need space" they have found someone else. The only exception for this is if you messed up really badly and physically or verbally abused her. The last thing a person "in love" wants is space from the person they supposedly love. It's like saying I love eating pizza, it's my favorite food therefore I won't order anymore of it.
I suggest you jump ship before it hits the ice berg. As I said above there is a tiny tiny chance of getting her back but you have to act fast and be strong. You have to cut contact for at least several months and focus on becoming a better man. Focus on becoming more muscular, more confident, richer, and more popular. Improve yourself and become better. Thats what I'm doing. You are going to feel powerless, but in reality you will be in complete control. Take it from me, I didn't follow this advice when it was given to me months ago and I'm paying for it dearly.
Don't take this personally either. You simply lost out to another man, it happens so don't be bitter about it. My plan is to improve myself so much that no matter how perfect my ex's next bf is, I will be superior to him in every way humanly possible. Even if I never see her again Knowing that is all the revenge I will need.