Reddit just loves vengeful behavior towards a cheater and doesn't care how it impacts the kids.
You are confusing two things. You can actually say "It is not your fault" without a message about the fault. You can also say "Sometimes things happen in a marriage that leads to the parents not being in love any more and needing to divorce"
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Ta da!!!! No blaming.
It isn't that hard.
Here are some resources for people going through this who might be interested in actual reliable information:
The Sandcastles book was a really good one for me and covered many things I had not considered.
You and your ex-wife are both the assholes.
It's easy to isolate this one situation and ask AITA. You and your ex-wife are a continuing source of anxiety for your son (and probably for all three of your children). You have no idea what is going on in his head but six years old (his age when you split) is the PERFECT age for your son to think the divorce is his fault. I am sorry to be so harsh here but you cannot pat yourself on the back for not being the asshole this time when you admittedly are acting like a child in regards to communication with your ex.
I get it. You would not be divorced if your needs were being met. There is a lot of baggage for everyone who gets out of a failed marriage - especially with children. However, your interaction with your ex is no longer about the two of you, it's all about your kids (and nothing else matters). You can deal with the wounds inflicted during your marriage on your own time. I fear the turmoil between you and your ex are inflicting wounds currently on your children but, given his immaturity, only your 8 year old is showing it.
You and your wife chose to have these three children and you are their family - divorced or not. You owe them because you have a responsibility to them to figure out a way to interact in an adult and civil manner with your ex. Be aware, however, all of your children are watching. If do not figure out how to have polite and civil interactions with her, ALL of your children will see just how easy it is to pit mom against dad. ALL of them will see that DAD is being unreasonable and won't talk with mom. Since you have such little time with them, you will probably lose in the end. If she's the one who is being unreasonable, keep trying. Keep being civil. Remember, you are not doing it for her (as I assume she actively tries to push your buttons), you are doing it for your kids and they deserve at least one parent who is going to put them above the pettiness hungover from that marriage that ultimately ended up in a divorce. If she is actively pushing your buttons, you won't need to call her out on it. When your children become teenagers, she will be called to task on her behavior for about 5 years in each of your children's lives. Depending upon how many years between each of your kids, it could be a very long decade...
When I was going through my divorce I was given a book. It helped immensely. https://www.amazon.com/Helping-Your-Kids-Divorce-Sandcastles/dp/0679778012/ref=sr_1_1?crid=327XE9YN7O11Q&keywords=divorce+the+sand+castle+way&qid=1560203461&s=gateway&sprefix=divorce+the+sand%2Caps%2C246&sr=8-1