How to win her back

[KingWing]

So in March I started a relationship with someone that I worked with. Everything for the first 2 months was brilliant, like a pure whirlwind. Things moved fast and I felt like we connected on every level. We have loads in common and both have/had the same vision for the future. She told me that she loved me and that I complete her, she also asked me never to leave her. We had contemplated moving away together, looking at houses and getting a mortgage together. We have booked holidays together and everything was perfect. Then 2 weeks ago I noticed a shift within her behaviour towards me, she was never angry or anything, but seemed to put distance between us. We would always cuddle in bed, but then she would decided she didn't want to. Then on Monday she told me that she didn't feel the same anymore, she told me that I was amazing as she broke it off. She also said that she wants to be in contact and ge friends. This has left me feeling confused about how things can change so rapidly between us.
I have since spent time this week reflecting upon events that have occurred between us, but can't pinpoint a reason that things would of changed.
The only event that I know has happenned is a work related incident which had caused stress.
I have ordered books to gain an understanding of the disorder. Also spent hours upon hours googling trying to understand.
I have spent the week resisting the temptation to call/text her.

What do I do?