"Why am I seething with this animosity?"

In all honestly, life has gone very swimmingly for me over the past few months. I have very little to grumble about.
However, there is always one constant thorn in my side, one that I will have to put up with more many, many years to come; Temper Tantrum.

Obviously situations like the one I'm about to tell you about are often presented in something of a one-sided manner, no matter how even handed one tries to be.
To each & every person who may read this, I make a solemn vow: I have made no embellishments & there are no omissions, it is exactly how it happened.

Today the heinous & vile woman that I was somehow stupid enough to marry has really outdone herself.
See, Cutieboy was supposed to come for a sleepover with The Boy today. Sadly the poor mite has been ill today, so he couldn't come over. Once Dream Girl had furnished me with the news I immediately phoned Temper Tantrum.
"Oh dear" she said & then put The Boy on the phone. I told him what was going on & he was understandably upset. Bless him, being an only child makes school holidays a bit of a pain for him & he was really looking forward to having his friend over.
As he was getting upset & I was comforting him, I heard his mum telling him "not to worry, it's nobody's fault"
Then she comes back on the phone...
"It's not fair, it's always me who has to deal with him being upset at times like this", to which I replied by reminding her that she had just stated that it wasn't anybody's fault & asked her to "please, don't take it out on me". This was met by a short rant about how I don't understand because I'm not with him all the time. This rant was polished off by the following direct quote:
"I am his 100% sole parent".
I immediately hung up. I was livid & incredulous.
I texted her thus; You are NOT The Boy's 100% sole parent & it makes me sick to hear such utter toss.
When I told some of my friends at work what she had said, they simply couldn't believe what they were hearing. Buddy With Boobs was particularly incensed as she knows how much of myself I willingly give to my son & how hard it really is when the other parent contributes very little.

When she brought The Boy round earlier I asked her what time she wanted him back & closed the door as soon as she answered.

An hour or two later, she phoned. She asked how The Boy was & I told her "fine".
She then said "If you hadn't hung up earlier I was going to rephrase my remark" I interjected straight away to tell her that unless what she had to say was directly about The Boy then I didn't want to speak to her.
This showed me up to be "pathetic", apparently.
I hung up.
She phoned 2 or 3 more times but I didn't answer.
She then sent a text pointing out that I was childish as well as pathetic.
I replied with 2 words, the 2nd being "off".

I really do hate the woman & with every one of these incidents she further erodes all my memories of us once being happy together. Worse than that, I have found myself having much less patience with the son that I adore today.

If she thinks I'm going to let this go without a massive apology then she is as deluded as she is despicable.