She really turned his head that’s for sure.
I’m not saying it’s her fault - not at all - it takes 2 etc. But I just think for my sake he could at least pretend to be over her if he wants marriage to work.
You have no evidence whatsoever that he wants the marriage to work.
In fact you have mountains of evidence to the contrary, some of it direct admissions in his own words (he still loves her and pines for her) and some of it in the form of his disgraceful treatment of you.
Going to marriage counseling is not evidence of wanting to sort things out and find a way to move forward. Your H is in counseling in order to prove to the counselor that you are a horrible woman who has blighted his life and won't even give him a shoulder to cry on now that his only chance at happiness has been snatched away. The counselor has bought his narrative.
When your decision not to continue with marriage counseling becomes known, your H will use it as proof that you are unreasonable/ cold/ selfish/ have checked out of the marriage. The counseling is a mind game he is playing. Don't engage. Try not to be affected by any lies he tries to tell about you. Practice indifference. Your H is going to tell lies about you anyway - you won't win any of the games he is playing right now. He has set you up to lose and while you're at it, play the role of personal garbage can and emotional punch bag too.
Emotional detachment, why and how:
www.theneurotypical.com/emotional-detachment.html
For all their crocodile tears and hyper-sensitivity, abusive narcissistic, borderline, histrionic and sociopathic people are emotional predators and bullies. If you stay in the relationship, the best you can expect is more of the same. You may achieve some periods of “peace” (remember, they say they are not responsible for their behavior; you’re responsible for their behavior and your behavior and all the other problems in the universe), and maintain your boundaries.
“Happiness reflects the difference between what you expect versus what you actually get in life—so if you keep expecting good things to happen, but they never do or take a turn for the worse, you will suffer constant unhappiness.” (Sutton, 2007, p. 134) Your spouse is abusive. They probably have significant characterological pathology and are unlikely to change. Therefore, keep your expectations for their behavior low, but continue to believe that you will be okay once you remove yourself from the situation and/or stop giving them the power to hurt you.
6. Do something that removes you from the abuse and centers you. Meditate or whatever your version of meditation is—reading, walking, woodworking, painting, music—anything that’s restorative. Find pockets of sanity and safety with friends and family or physical spaces like your office, the gym, the pub or social/professional organizations. Find activities that will take you out of the line of fire and minimize your exposure to them and their abuse. Find a hobby or activity that makes you feel good about yourself and restores your confidence and esteem. Ignore them when they become jealous or puts down these new activities and friendships. They do so because they see them as threats to their control.
7. See the big picture and don’t get distracted by their minutiae. The ultimate goal is to not let their abusive behavior effect you anymore and to end the relationship. Expect them to hit even harder—emotionally and/or physically—when you stop reacting to their tried and true button pushing. It seems counter-intuitive, but if they become nastier in response to you setting boundaries and detaching, it means your new behavioral strategies are working because they are fighting harder to retain their control. By detaching, you’re taking back the power that you unwittingly ceded to them.
These new behaviors will take time for you to learn and perfect. It takes a while to develop indifference. It runs counter to our fundamental beliefs about love and relationships. However, if you’re in a relationship with someone who verbally and/or physically attacks you, devalues you, makes you feel less than and who raises themselves up at your expense, you must learn how to make yourself less vulnerable and eventually immune to them. Abusive neurological/biological disorders have no soul and they will destroy your soul if you let them.
Check out the whole article.
You are ahead of the game in one really important respect - the two of you are living separately.
What is holding you back here is dread of pulling the plug. It's not fair that he landed this information and responsibility for the decision that arises from it into your lap, but as many PPs have advised, go to a solicitor and see where you stand so you can at least see more clearly into the future. You don't have to act on the legal advice immediately.
Get counselling for yourself.