You are about half-way toward answering your question, "How do I get past this fear of standing up to him?" I think that despite your fear of standing up to him, you may actually be fearful of hurting his feelings deeply and undermining his self-view. I think you realize that unconsciously, he escapes and avoids responsibility for many of his misbehaviors by blaming his history. For example, unconsciously, he has always insisted that he has cheated on you because he was an abused child; or because he was an abused child he now fears being vulnerable and won't take emotional risks or can't emotionally commit. So, I don't mean this unkindly, but you have fully bought in to the self-pity story he relies on to act in an incredibly disrespectful manner toward you.
I think a switch is being 'flipped' in your head, finally. After all of these years, you are finally realizing that you excusing the behavior of a man over the age of 50---a fully grown adult, by blaming the fact that it is all caused by his difficult, abusive childhood. The way you are enabling his behavior is by treating him like an abused little boy who really isn't responsible for his actions. For heavens sake, the man is over 50 years old! How much longer will he, or you, blame his childhood for his PRESENT behavior, 50 years later? Also, the truly abusive aspect of your relationship e.g., being disrespected and cheated on over the years for instance, is something you've also enabled. That is, so long as he knows you will NEVER leave him, then he can continue to firmly believe that he can do most anything, and treat you in most any way he wants, and you'll just sit back and take it. He can misbehave, do what he wants, and then apologize and appease you. You'll forgive him because you want to believe he is sincere and you want to excuse his behavior based on the fact that he was abused and unloved growing up. This is of course, completely irrational and an irresponsible thing for him to do.
I'm going to share a secret with you regarding how to start disrupting your pattern of treatment and interactions with him. You won't want to believe it, nor do I expect you will start living it, because it is quite hard to do. But anyway, here is how you are actually enabling him to treat you as he does. You believe that by being loving and kind FIRST, such 'loving and kind' treatment will cause him to treat you well in return. This core belief about human nature and behavior is similar to what you see when a father gives their irresponsible teenage daughter who is failing school a new car and says, "Now that I've been so nice to you and given you this car out of love, I believe it will cause you to suddenly start getting better grades." Nonsense, of course. What the father should do is agree that he will put small payments toward a car in an account AFTER the daughter improves specific grades in specific courses. Once her grades have been maintained at a high level once again, for say a one year, he THEN gives her the car.
Here is the hard part----the irony of your relationship in my opinion, is that your husband's behavior can only improve if you are actually willing to leave him, if he DOESN"T improve. That is, instead of beating your head against a wall, expecting that if you are loving and kind, he will change, you need to start doing what the father does for his misbehaving teen who is getting bad grades. That is, I would suggest that you announce to him that you are tired of your years of mistreatment and the cumulative effects of being disrespected and cheated on. You outline 2-3 specific behaviors that absolutely, positively must change in the way he relates to you or treats you. You tell him that he has 30 days to make these changes, or you will file for a legal separation from him. You take back control of the direction of the relationship---doing the complete opposite of what you have done in the past. Nothing of what your therapy, your book reading or anything you've been 'taught' has helped, right? So, you basically say, I'm taking control of my life in this relationship and that means I'm not going to be abused or mistreated emotionally in these ways any longer. You need to change. If you do, I will THEN react to you with support and further commitment. If you do not change, you can live your life alone, without your daughter and me. I'm done being loving, kind, jumping through hoops, HOPING YOU WILL THEN START TREATING ME WELL. The rules have changed. You need to change and show me you are worthy of having me continue in this relationship, and if you do, I will THEN be supportive, loving and cooperative. If you start mistreating me again, I walk. I'm done treating you like an injured little boy, whose behavior, even at age 50+ needs to be excused because of your bad childhood. You are a grown up and need to start treating me with respect, if you expect to have my companionship in the future. At this point, I will give my love and support to you only AFTER you change. If you do not change, you will not receive any of me.
What do you think?