Unfortunately feeling this way is normal for want of a better word for up to six weeks.
The best thing to do is talk about it as much as you need to - over and over again.
I recommend you get in touch with Victim Support who can allocate someone to give you support.
And bear in mind that your DP has a vested interest in you pulling yourself together - a lessening of his guilt - after all it was his ex-P who did this.