I applaud your efforts to understand your part in the affair and to hold yourself accountable to changing and becoming healthy. You are so very right that setting about to better understand yourself will benefit you no matter the outcome of your marriage.
It is only natural that you are not 100% sure whether you want to reconcile your marriage. Considerable damage has been done. Certainly your husband's actions and attitude are an affront to a 20 year marriage! Knowing if he has the motivation and capacity to be that trusting, loyal, and loving man of the past is an uncertainty.
I agree that getting him into counseling - whether individual or couple - is necessary if there is to be any hope of reconciliation.
Because you cannot control his behavior or make decisions for him, all you can do at this point is to ask him.By pointing out how you believe it has helped you perhaps he will see the benefits.From what you wrote, he does sound ambivalent about his current status. Whether that ambivalence is enough motivation is another question.
In the meantime, I encourage you to remember that you have only one life to live. You have made significant steps in seeking a healthy lifestyle marked by honesty and transparency. You have much to offer to a loving, respectful, and committed relationship. Choose your future wisely.