I had a sleep monster and some posts like yours. Sometimes you have to walk away for your own sanity. Even though you know that tantrums are usually frustration and that your child needs help, you can't regulate them if you are not regulated and calm yourself.

FWIW, it ends. It does. What I found helpful was to tell Liebling, over his protests sometimes, that Mamma was tired and needed a drink. I love him very much, and I'll be back after I have a cup of coffee. Sometimes I would "race" him: I reckoned he couldn't go to sleep before I finished my coffee. That came later though.

So I sat and had a coffee. Then I went back, a little more refreshed, and held him, kissed him, let him know he is loved. But it is still sleep-time. Sometimes I would tell him I was outside his room. I would pick a book I enjoy, but wasn't inappropriate (so think Roald Dahl over 50 shades LOL) and read it in a calm voice. Liebling knew I was there and if he needed me I would go in, but he could hear me and that really helped him.

He can now put himself to bed when he's tired, goes to sleep on his own and loves bedtime. This started around age 4, so before he went to school. But it was a bit of a nightmare before that. My attitude was always "when he marries his wife can get him to go to sleep" - so any sleep satisfaction I have before he moves out is just a bonus and I enjoy it. (But that was in response to the "rod for your own back" comments you have doubtlessly been attacked with recently, going by your post.)