OP - your post really resonated with me.
I tried so hard, for several years, to make a marriage work with a DH who was just detached, distracted and innatentive. He insisted that nothing was wrong and my expectations were too high. He refused to leave but he also refused to change or engage with me really. He once said "I'm unhappy in this relationship because you keep asking me to leave". Again, turning it on me!
Eventually I gave up and he agreed to leave. He didn't put up any kind of fight for me at all, although he was angry at me for a while (because I asked him to leave).
Six months down the line, we are on relatively good terms with each other. He now admits that he was deeply unhappy and felt we were unsuited (which we really were!)
He also said he respects me for being the one to actually end it, because he is a passive person who would never have faced up to it.
It has been very hard at times, especially with young DC who were very upset when he moved out.
Overall though, it is like a weight has been lifted from my shoulders.
I have started dating again and met some really lovely men, no-one I have clicked with enough to keep seeing but it is still good to meet new people (there are a lot of decent, divorced men around who are hoping to meet someone, way more than I realised!).
Some people were surprised that I was ready to do this so soon , but having been in a dead, lonely marriage for so long, I was over the grieving part quite quickly, as I'd been doing that for a long time before we officially split.
You cannot make a marriage work by yourself. As another poster said, you don't need permission to leave, not from DH and not from anyone else.
In a relationship, you have the right to ask to have your needs met. If the other person will not, or cannot, meet those needs then you have the right to leave.
Good luck with it all.