From what you are saying it really really looks like he is walking away and you are pursuing. Pursuit does not work. It is completely counterintuitive, I know, but that is how it is.
When my W was in her EA (...who knows, she may still be but I don't think so), I tried, really tried to get her to read some of the marriage fitness type books with me. It failed completely!!! She would drag her feet, refuse to talk, roll her eyes, etc. I also pressured her into MC where I would open my heart and talk, but in which she would simply shrug her shoulders and answer "I don't know" to any question asked of her.
I realized later that during every minute of this she was sitting there thinking "I just want to run away, I just want to run away, just get me out of here..." Everything I was doing - all of the pressure to work on the M, was just reinforcing her desire to leave. She wasn't thinking logically, she just wanted to escape.
During this time I got all of the same things your H is telling you now. "Our M has never been good", "I have not loved you in x years", "I need to be with someone who is fun, and you are just not a fun person"
Now remember, these things are not necessarily true. Don't let him steal your positive memories of the M and try to make you feel like your married life has been a lie. however, you have to realize and really really accept, that in your H's mind, they are true.
Think about your R with your H as having 2 components. 1 is the basic friendship and partnership. This is the R where you care for your son jointly, work out finances, spend casual time together, etc. - Call it "Partnership" if you will. The other is the loving, intimate, romantic, mutual attraction part of the R - Call it "Romance".
In your H's mind (and in my W's), the "Romance" part of your R is DEAD. He believes that it can never come back, and that any attempt (counseling, books, etc) to repair the M is an attempt to force emotions that can not be. In fact, it is worse than that. Since he is convinced that he is not attracted to you, he finds the fact that you are holding on and trying desperately to work on the M to be unattractive! The more you hold on, the more he wants to run.
It sucks!! it is unfortunate! I hate it! It is not logical!! It is not realistic!
...but that's the way it is.
Accepting this is enabling me to a) take the pressure off my W, and by doing so to slow her flight. b) stop driving myself crazy with efforts to revive the "Romance" part of our R. Those efforts were just alienating her while at the same time increasing my own emotional attachment and desire. c) focus on my efforts to improve myself (believe me, I need it) d) work on improving the "Partnership" part of the relationship.
I am in this the same way you are - I'm no expert. I do, however know exactly how you are feeling. It is really really hard to let go of the Romance part of the R.
I wish you strength, I really do. No matter what happens, this is going to be really hard.
We are all in it together. Take care of yourself
-Thinker
Me 42, W 39, S8, S6, S2 M 11y, A & ILYBNILWY 11/08 Walking away from a bad situation.