From the 12 steps of AA:
9. Made direct amends to such people wherever possible, except when to do so would injure them or others.
Some people go through life wanting to hide from the truth. If your W is like that, I'd suggest finding some way of ascertaining if she wants to change. IMO, the change is entirely worthwhile, but your W may not be willing to do the work.
Still, if your W is in her early 50s, too, she's looking at a median life expectancy of 30+ years, and the work will take, probably, 2-5 - and some of the payoff may come within the 1st year - so the ROI can be tremendous, especially since life expectancy is much higher for people who can afford good health care.
*****
If your W doesn't want to hear about your A, a good IC can help you deal with your sense of guilt and refusal to forgive yourself.
IMO, WSes heal by changing from cheater to good partner. You've done a lot of that. What's missing, IMO, may be being as honest with your W as she wants you to be and being ruthlessly honest with yourself.
I think you may be ruthlessly honest with yourself, but you don't yet know how honest your W wants you to be with her. My reco is for one of your IC goals to be to figure out how to ask your W about that in ways that will get honest answers.
Musing here - my bet is that she shows emotions in ways you don't recognize or stuffs them. Your description says she probably stuffs them. Unstuffing them is generally not easy. I hope she shows them in ways you don't recognize.
*****
Many of the things you say - addiction and thinking you know what your W wants and thinks and 'would do if' - are hall marks of co-dependence. For that reason, I suggest readin things like Co-dependent No More and the 'Drama Triangle'. Steve Karpman is the best voice on the DT, IMO, and he has a website, but I recommend only the free stuff on the website - like his original Drama Triangle article.
*****
There's no doubt in my mind that confessing to your W will unburden you. I just fear that confessing 20 years after the fact will transfer the pain from you to your W. I agree you owe her something better than that, and I believe you can do what is needed to serve both of you..
*****
I do my best not to judge. Terseness saves keystrokes, which I deem important.
[This message edited by SI Staff at 7:33 PM, Saturday, March 29th]