I've had similar conversations. H: It's about hopelessness, never trust you or this relationship again, I'm "past" anger, only sad because of losing you, our love, our dreams, everything, what we had (yet what he feels we didn't have ALL THE TIME and thus could not tolerate),and other similar things that you posted above. Your H was unhappy, identified you as the cause of his unhappiness, and thinks he will get "happy" alone or with someone new. In this new future, the woman will never have anyone die, never get sick, and, if she does, she will not be distant, moody, critical, or grieving, she will be a non-stop dispensing love machine who will make him "happy." Unlike you. She will turn life's stress, hers and his, into cotton candy.
That is my take of it. With some guilt sprinkled in. When I have gotten similar speeches (granted I expanded liberally on the grass is greener subtext, but I'm just extrapolating from the actual words and overall vibe).
This is not a 2X4. It's my interpretation of where you're at and it is partially where I've been (or am?) at times.
It is also the "reframing" offered in the "good divorce" articles in books and on the internet. Hey, no responsibility, no blame. We're both in a "different place" now. Let's be friends. What "forever"? I'm sorry you feel there was a forever and then broke your part of the cotton candy contract.
As far your your husband's depression, yes it colors everything. Especially the hopelessness to fix part. But it gets tricky because you also can't tell if it's just someone who wants to date and is depressed because he feels guilty about that. As he said, anger would make it easier because anger is energizing against depression and tamps down the guilt that he feels because he actually DID tell you he wanted to be with you forever. You're not making it up. It happened. He wants to erase it, for whatever reasons.