I would also suggest you look into private therapy for yourself. I would suggest you look for a therapist or an addiction doctor (most work with family also) and find one that is familiar with the CRAFT (community reinforcement and family training) method. This has a dual purpose – It is designed to improve your life (stop the financial and emotional toll his addiction is taking on you) by teaching you not only about enabling behaviors but also creating boundaries that fit your life. This is similar to the Nar- Anon approach, but CRAFT believes your love does have power… you cannot cure him of his addiction because it is a medical problem. You couldn’t cure him of cancer either… What he needs is professional treatment (individual therapy, or in this case with a 20 year dependence most likely inpatient rehab followed by continued care). CRAFT can teach you how to maintain a caring and supportive relationship while using positive reinforcements that encourage him to want to enter treatment. It has proven results at increasing the odds loved ones will enter treatment. I think it is like 7 out of 10 people have success. Once he gets into treatment then it is up to him to do the work.
When my husband was in rehab, the therapist introduced me to the methodology, and I have used it to support my husbands early recovery. She also suggested a book on CRAFT called: Get Your Loved One Sober Alternatives to Nagging, Pleading, and Threatening, By Robert J Meyers PhD.
You can google CRAFT, and the book.
Private therapy was a HUGE help to me and I always suggest this if you have the option; I learned so much about myself, about addiction, and it is something I will always be grateful for. My husband and I did start marriage counseling when he was about 6 weeks clean and in rehab. I think it is positive that your husband is attending sessions with you – No it doesn’t sound like he is fully engaged, but he is showing up – that is a lot more effort than many addicts / early recovering addicts put forth. I learned a lot from the marriage counseling sessions & it opened up more questions for me that I in turn talked about in my private sessions. The two go really well together IMO.
The other thing I would suggest if you have not already done so is read up on addiction from a medical perspective, how it affects the brain, the symptoms of disease such as denial, lying.... a good place to start is National Institute of Drug Abuse as they have info on everything, and offer advice for families. Your post about his being a pathological liar really fits... he has been an addict for 20 years and lying ( a symptom of disease) has become his norm in order to protect his addiction, and help create an identity that is not necessarily true to who he is...
Whatever you do remember the oxygen mask rule: if you don't attend to your needs first, provide yourself with "oxygen" to live your life, then you wont be able to offer assistance to anyone else.