My IC (whom is really great) started therapy by teaching me skills and the methodology (like learning to play tennis) on how to cope with the "reality gap" between the reality I want (and knew), and the reality that is delivered to me with my H's MLC.
Now that she sees that I am progressing well with my coping, she has started to focus on helping me try to better understand H and his MLC. She agrees that the more I understand "what is happening to H", the easier it will be for me to accept the new reality. This exercise is of course not the same as H going to therapy, and analyzing him (through my eyes) is really to help me (not H). Here is what we did in the last two sessions - happy to share further reading materials.
Attachment Types. The first thing my IC wanted to identify was our attachment styles - here is a test I found online:
http://www.web-research-design.net/cgi-bin/crq/crq.pl. See here for short explanations on the different styles and their impact on relationships:
http://www.psychalive.org/category/attachment-style/ and
https://jebkinnison.com/bad-boyfriends-the-book/type-dismissive-avoidant/. She asked me to answer the questions positioning myself at a time (i) before I met my H (my natural style) and (ii) 6-12 months before BD (to see how his style impacted my natural sense of security). She asked me to do the same for H, as best I could, and to survey his old friend/family for the time before he met me.
It was very revealing. In my case, H was clearly very Avoidant/Dismissive before he met me, and became more Secure when he met me (probably as secure as he could have gotten), because I am very Secure and I figured out intuitively from the start that I needed to give him lots of space and freedom, while being supportive and emotionally available. Summarily, a person with Avoidant/Dismissive attachment fears intimacy and rejection, and copes with this fear by training themselves to not need to attach or connect with anyone. She suspects that once he shut me out and shut down that source of emotional security, he reverted back to his natural attachment style of very Avoidant/Dismissive, which is where he is most comfortable to weather his existential crisis - or vice versa.
This reassures me that I did the right thing all these years by giving him space instead of trying to demand more intimacy and forcing him out of his cave... Maybe this was the maximum amount of emotional connection that he could have sustained (until he deals with his childhood baggage). Maybe he ran away to be alone, to not have to need me, nor for me to need him. This may also explain why he ran away even if there is no OW.
Schema Therapy. The school of psychology I am workinh on is called Schema Therapy; the forefront of that school is Jeffrey Young see
http://www.schematherapy.com/. I read his easiest book "Reinventing your Life", and it helped me identify the Schema (i.e., the warped filters through which we interpret information and act) that was controlling my life (and that of H) and how to work on neutralizing them to live a more authentic life.
We are all "warped" one way or another, and we kind of have hints and impressions that we are warped, but may not have consciously realized or acknowledge the warping or its impact on our lives. Very quickly, my warped filters were named and I understood how influential they were on my way of seeing things and how they contributed to my knee-jerk reactions and how they impacted the actions and decisions that I took.
This is heavy stuff and will take some time to work through, but understanding the existence of the filters (and that they should not be trusted), naming them, and facing them, is good start. This exercise helps you to better understand the inner workings of yourself and those you love, including H.