Grieving a relationship

I was in a relationship with another woman for roughly 3 years. She had a daughter aged 1 when we met. We took things slow and I was hesitant to be with someone who had a young child. Fast forward to 3 months ago, after my fiance and her child moved in with me, after years of being a full time parent to a child that wasn't mine, but loving her and feeling fulfilled from having a family for what felt like the first time in my life, she leaves one day without any warning or conversation. Her daughter was visiting family when this happened. I never got to say goodbye. I feel so absolutely empty and heart broken not only over my partner leaving abruptly, but the absolute loss of her daughter that I regularly took care of for 3 years. Watching her grow and learn to talk and get smarter. Just really putting my all into this. I feel like my entire world has been shattered and I'm struggling to even make it into work. I don't want to feel like this anymore. I feel worthless.