I know it probably is not a good idea to tell him that I know we will end up together but it's just how I feel.

It may be the way you "feel", but it's still not a good idea to act on it unless you want to give him more reason to pull away. We all feel like doing things sometimes that wouldn't be in our best interests, not just concerning these sitches but in other facets of life, and we reign them in in order to try and get the results we'd like.

H telling you that he doesn't think you can act sane, or at least his definition of sanity, and of being a suitable life partner, is a clue that time and consistency in behavior is required if he's to change his mind.

Actually it's what I know. I don't really know how to explain it, but deep in my heart I know that despite everything my H and I will be able to pull things together.

Obviously, this gives you some degree of comfort and peace, yet no knows what the future holds and as a basis for comfort and peace, I think having a workable plan achieves that as it gives you something tangible that may produce results.

His going to counseling contingent on you signing a separation agreement doesn't thrill me; it's not a solid basis for seeking counseling. Sounds more like he's trying to get you to sign the agreement, and maybe he'll then cancel or tune out of his end of the bargain afterwards and deal with the fallout then, but he'll have your signature on the agreement.

Don't ask him for "another chance", he's not going to give you one and asking for it is pursuing and will push him further away because it makes you appear clingy and needy to him. Instead, act as if you've already been granted that chance, acting in accordance with it, demonstrating by your actions as time goes on, rather than trying to convince him by word or appeal. Don't listen to his saying "It's over, move on with your life"... that's WAS verbiage you can disregard insofar as he may feel that way this moment, but again, the future can be different. He's just trying to dissuade you, and that's because you're pursuing him. Stop the pursuit, and his guard will correspondingly likely go down. Don't ask him to do things with you, go about your own life.