I am so sorry. You must be crushed. It's okay to be a bit of a wreck for a while. Your world is different now and you can't resist your feelings of loss. Accept the sadness, let yourself ugly cry yourself to sleep some nights if that's what you're feeling. Shaming yourself or letting other people shame you for your sadness will make the whole process of moving on take a lot longer.

That being said, try not to preoccupy yourself with your sadness either. Now's a good time to get lost in your work/hobby during daylight hours and/or reconnect with some friends so you don't drift too far over to the dark side. I do my most/best work right after a break up. You've got a max of 3 days to sit in darkness and do nothing but eat ice cream and watch netflix logging (I don't think that's the right spelling) all of the things that remind you of her (or whatever is the equivalent grieving impulse). Anything more than that and you're developing bad habits.

Brighter points. It's going to get better. It's an inevitability that you will feel better and better as time goes on and your world is full of possibilities that weren't there before. You're not going to feel worse than you do right now and it's better that she left now instead of another year or two down the line, or worse, after marriage.

I hope this helps. Pm me if you need some big titty pity nudes.