Heartbroken

So my ex said he wanted to take a break for about a week. (He said this a week ago) and I made the mistake of texting him last night saying I missed him. He replied saying he has moved on and we shouldn't talk.

I don't know why I'm so heartbroken. We only went out for 2 months. I can't think about anything else but him. What should I do ? Is this normal ?