Have you seen a solicitor yet? I haven't followed things that thoroughly, but you seem to be making lots of assumptions about what will and won't happen in the future, then thinking you need to make decisions right now based on stuff that may or may not happen.
It upsets me to read that you think you need to "eat humble pie" about anything.
You say you will not risk losing your children, or making them choose between you and your H (as they might not choose you.)
Thing is, whatever you do or don't do, you may still "lose" your children. You can't put a bubble around them to make them do what you want or don't want forever. You can't actually shield them from what is happening to you and the pain of their parents being in a miserable relationship.
You may feel that it's better to stick your head down, put up, shut up, remain the doormat, paint on a smile and think your children will think all is tickity boo, that they'll stay with you, that you can protect them from their father's ghastliness.
But, they are watching and learning all the time. They may work out that their father is a 24 carat dick and decide that they want nothing to do with him, or think he's great for a while then realise he's a turd. Alternatively, they could be learning that this is how relationships are "supposed" to be - men are the "Big I am" and call all the shots, women stay under the thumb, do skivvy work and are treated terribly.
My sense is the longer they experience parents in such a toxic relationship, their mother being so down and downtrodden, their father being so blase and arrogant, the more they will "normalise" this and not question it. Some day, there may be daughter in laws who experience life just as you are now.
The point is, what you do or don't do may make NO difference longer term to whether your kids stick with you or not, but the longer you stay in the situation you are in now, the greater the chance that your sons will see their father's behaviour as normal. If you don't question or challenge it, why should they think there is anything wrong with it.