I'm in a similar situation, with regards to an ex. I try to put it behind me, but it's not always that easy, and it/he does play on my mind more often than not... which is annoying.
It's harder when there's kids involved, as you can't just decide to never see them again. Meh.
Try to focus on the positives Meg, the fact you're doing absolutely fine on your own and don't 'need' him, the fact that your health is good and that you're secure in your job. They are all really good things to feel positive about.
I'm a bit of the opposite to that, I kind of fall apart when I'm on my own. Actually, I'm probably the worst person to speak to about this. I'm a lost cause! Lol :D
Cognitive therapy is good, but I found as soon as I stopped, I just went back to my 'normal' ways. Normal being not normal at all :)
I don't actually have any books, but I do have lots and lots of printed out sheets of paper that family members have given to me. I keep them in my bedside table and have a read of it when I'm feeling anxious.
There's lots of info online regarding anxiety and ways to 'beat it'.
Sometimes it gets to a point where I'm in tears, it eats me up that much.
More often than not though, it's just a pain in the bloody arse!
I don't get like it every single day, and it's much more likely to happen when the kids have gone to bed and I'm on my own, but either way it's not very nice and it does get a bit 'controlling'.
Next time you're thinking that something bad is going to happen, as a result of you not doing something, give yourself a good talking to.... out loud if no one's around. You may laugh, but a fellow panic attack sufferer once told me to do that, and it does work :-)