@BreadInCaptivity I think you have a point about the effect of his marriage, but I don't think you can pin it all on that, and I do think that childhood traumas crystallise responses in adulthood that just take you back to that stage of (arrested) emotional development.
Pre Meghan, Harry was already in therapy. He has said he was really struggling and that William recommended he go. William. Harry and Catherine launched Heads Together in 2017. I think being part of the threesome with W&C was giving him purpose and direction, and I get the impression they were handling him and keeping a lid on what was going on underneath. Invictus was a joint enterprise between the three of them originally through the Royal Foundation and effectively gifted to him as a solo project to spearhead.
He said in Spare that he has been diagnosed as having an addiction to hatred to the media and wanting to right the wrongs against his mother, as @Mummyoflittledragon wrote:
There was also a lot of discussion on MN the time Spare was leaked that Harry may currently be receiving the sort of therapy, which encourages the client to seek reparation from those, they feel have wrong them in order to heal. This can lead to more trauma when a person feels rejected once again.
If part of that therapy includes his stated aims of Archewell, as per the extract from their webpage linked above by @Lunde , the frankly frightening attacks on free speech he is advocating with the Aspen Institute and his plethora of court cases against the media, then he engaging wider society in his theraputic process - and not from any position of particular insight or expertise in the field. He's doing it from the standpoint of, imo, an angry (and frankly, stupid) little boy who is absolutely fixated on his mother and what happened to her, and, by extension and with causal blame shifting, everything that has happened to him.
He appears to have done nothing to try to see Diana as anything other than a martyr and the mummy he knew as a 12 year old. Part of therapy about one's parents should include seeing them as human beings, flaws and all, to try to understand them from your point of view as an adult, and to try to see less black and white and more shades of grey (I'm not talking about extreme abusers here - just the generally negligent and incompetent ones). It's part and parcel (to me, anyway) of absolving yourself of any guilt and responsibility for what happened to you in childhood, the way your relationship with your parents panned out and their own current state of being He doesn't seem to have thought at all about Diana's own responsibility. And he seems to want her reborn, to pick up where she left off, in Meghan (and possibly, lord help her, his daughter, whose physically visible Spencer genes he rejoices over).
MM, I think, just let the genie out of the bottle, that the Firm was more or less successful at keeping a lid on. It benefits her in every way for Harry to believe and portray her as Diana 2.0 (whether or not she believes it herself), and it benefits her to have a seat at the table - only bestowed through her husband - in high level, political discussions on free speech and mental health. If he moves away from those discussions, if he stops using wider society as his therapy session, then he has very little left to offer to stay on the big stage - and by extension, neither does she.