And you ARE witty. Darkly witty. Which is on a par with my sense if humour.
You don't need CBT, Mosman, you need a diet. One where you lose 13 stone (guessing!) of useless lard. The quickest diet that achieves that is a divorce.
Seriously, stop questioning yourself. It isn't about YOU. This is part of the script that ALL cheating scumbags use, to try to deflect THEIR guilt.
They find all manner of frankly stupid reasons for why they cheated, usually putting down the person they have cheated on.
In their brain, it 'excuses' them from staying faithful.
In fact, there IS nothing wrong with you, apart from your STBXH.
He is what was wrong with your life, and I can guarantee you that in a short time, you will feel like a new person, without him dragging you down.
For months, during his affair, he will have been 'demonising' you in his head, to try to justify his betrayal to himself. None of it is true, it is just HIS way of assuaging his guilt. Don't take any of it to heart.
Know that it is HIM with the issues, NOT you!