Sorry you are going through this. Most of us can relate to what you are going through.
I see you are struggling with wrapping your head around the whys: Why is this happening? Why is he doing this? Why does it have to be so upsetting? Why does it have to cause so much turmoil?
That is one of the biggest struggles we all go through. But here is the thing, the reasons do not matter. Nor will they help you. I know this is hard to hear, it was for me as well. When my most recent situation happened I struggled with the whys too, and then I had someone point out one simplistic, yet so profound, answer. And that is that he is simply trying to be happy. Why he wasn't happy no one can tell you, but the fact that he is doing all of this is in an effort to be happy.
I love your last question: "How can I make it through this, my friends? What can I do?"
The first thing you can do is come to the understanding that you are going to be ok. When you are thick in the despair of your situation it is hard to think ahead to 3, 6 9 months from now, or even a year or two from now, and realize that you are going to be ok! And if you think about it, you have no other choice. We live in an imperfect world. We do not get to decide the choices others make. Your H is making these choices, and there is nothing you can do about that. It is very similar to if he were to pass away. You wouldn't be able to change the fact that he were gone, but you DO get to decide how to move forward! And there really is no other choice to make. Remaining stuck in one place for too long is never healthy. So whether he leaves you, or whether he were to pass away, you should mourn the loss for a period of time....then pick yourself up and move forward! Likely there are other people in your life that need you, and it wouldn't be fair to them to remain stuck in a prolonged period of paralysis.
Second, once you realize that you are going to be ok, that you need to be ok at some point, the question is: how do you get there? First you start by taking your focus off of him, and onto yourself. Easier said than done, isn't it? But this is really a key piece to moving forward. This is going to be a culture shock for both you and him. But once you start focusing on yourself (and we'll talk about how you do that in a minute), then that culture shock will help you get over the fact that your MR is ending, and get you to a place where you realize that it is going to be much better than you could imagine it being right now! And it also means that he may not like the fact that you are moving on without him and suddenly decide to change his mind. You do not do it for that reason, but it could have that result. It has happened, though it isn't a guarantee.
In order to move forward you start instituting DB principles. Do not start R talks. When he does listen and validate. Do not accept disrespect, if he starts to get disrespectful you calmly but firmly end the conversation. GAL! Start living a life that others find interesting! Be busy, reconnect with old friends (preferably same sex friends), pick up old hobbies you may have moved away from, and take up things you've always wanted to do! 180 on any bad behaviors you have. Get into IC to cement these changes. If you are overly critical, work on that. If you are a pushover, work on that. Whatever your weaknesses are, figure them out, and work to correct them. Become the best version of yourself you can be! And finally learn to be lovingly detached. Get to a place of evenness emotionally, where he doesn't have as much control over what you think and feel. This starts by learning and knowing your own worth! Don't let your worth be dictated by other people.
One other point, Look back at your MR pre-BD. Did he have problems? Were you as happy as you could have been? BD has a way of making us, the LBS, romanticize that our MR was perfect before BD, when it wasn't. I know I was miserable in my own MR leading up to BD. If I am truthful there were many times when I almost initiated my own BD to my W! Yet after BD, I was consumed with trying to save it. While you may not have been as unhappy as I was leading up to BD, can you look back truthfully to say your MR was all you wanted it to be? I ask this because while the WAS will rewrite history that the marriage was always bad (yours did that), we often see LBSs rewriting history about how wonderful their MR and their WAS was too. I see you call him "my normally amazing" husband. Is that accurate? (Not a questions necessarily to be answered, but for you to ponder.)
"What is best for my kids is best for me" Amor Fati Link to quotes: https://www.divorcebusting.com/forums/ubbthreads.php?ubb=showflat&Number=2879712