You thought she was going to be miserable without you, and truth be told, she was. She didn't know what to do with herself. She didn't know where to go from here. She didn't know how she was going to get over this. That first week was the worst. She was going thru the worst relationship withdrawals, where she had the strongest urges to text you and pour her heart out to you to tell you how much she misses you and how badly she just wants to get back together. She had the strongest impulse to just show up at your house unannounced, hoping that she'd spend the night with you and you'll be back together by the morning. She had the strongest desire to forget and forgive everything that's ever happened between you two and just have a clean start because losing you reminded her of how much she loved you. A part of her knew she had to let you go, but another part her refused and didn't let her.
But as time went by, over the next few weeks, it got easier for her to fight off those urges and impulse and desires because she finally came to terms with herself that this is what was best for her. Sure, she's been lonely, but during that time, she was able to readjust to being on her own again and she was able to rebuild her life around without you in it. What? Did you expect her to just mope around at home? Did you expect her to dwell in the past and be stuck on you? Did you expect her to keep finding reasons to wait around for you? You wanted her to move on. You wanted her to get over you. You wanted her to not care. And now, she's slowly beginning to do all of that. Isn't that what you wanted? Isn't that why you two are broken up in the first place? Because you felt like it wasn't the right time anymore? And you wanted to figure things out?
Why are you starting to talk to her again? Why now? Just as she's making progress, you want to come back into her life and ruin that? What? Did you get everything you wanted to do out of your system as a single guy and now you're ready to be with her again? You think you can just manipulate your way back into her heart after shattering it?
There may have been times where you two were able to get back together, but not this time. This time, she's stronger than that. This time, she's better than that. This time, she's wiser than that. You thought she was going to be miserable without you, but in fact, she's much happier without you now because that relationship was beautiful at first and it was for awhile, but towards the end, it became dysfunctional and toxic and it just isn't worth it. There's less stress in her life now because you're not in it anymore. There's less drama in her life now because you're not there to cause her any. There's less insecurities for her to deal with because you're not attacking them any longer. And because there's less of all of that, there's now more of her loving herself and she loves enough this time to be able to tell you "I don't want to be with you".