At this point, I know that he is not frustrated with me, but rather with himself because he is unable to express things to me that he wishes he could. He has mentioned that he is not sure what he even feels anymore, and that he knows this is a result of supressing his emotions for his entire life. I sort of translated that to mean that it is difficult for him to speak things if he cannot put them into words - which does make me feel a little better, and helps me to not take it personally at least.
Sometimes, it's not a case of suppressing emotions necessarily. Maybe there aren't a lot of emotions to suppress. Some people are easy going, or resilient to a lot of things, and they just don't feel much sadness, frustration, etc. And maybe your husband feels these things, but doesn't pay attention to them.
If a man isn't "in touch with his feelings" is that really a bad thing? Is suppressing emotions really bad? Some things that get put in the category of 'suppressing emotion' may actually be healthy forms of emotional self-regulation.
I think you should also be very mindful of appreciating all the good things you love about your husband. Your last messages to me makes it sound like you are trying to do just that. What are a husband's duties toward his wife? One is providing for her. That's what a lot of men think. If a man loves his wife, is kind to her, and provides well for her, why wouldn't she be happy? Maybe this idea that he has to get in touch with the depths of his emotions and talk about them to please you blindsided him. He could also be hurt or frustrated if he thinks that you think he is lacking or doesn't love you, and if he isn't the type to be in touch with his feelings or talk about him, he may not tell you that.
In the Bible, what is a man's duty to his wife? In the Old Testament, a man is supposed to provide his wife with food, clothing, and sex. There is no commandment in the Old Testament that a man must open up and talk about all his past hurts, goals, visions, dreams. The New Testament tells husbands to love their wives as Christ loves the church, but it doesn't say they have to be in touch with their feelings to do this. The idea that he would be expected to share some emotional type stuff might not have crossed his mind going into marriage.
If you want to get him to share details from his past, if he's okay with it, I don't see why there would be a problem asking him questions. Maybe you could do that while doing something, like walking through the woods, or fishing, so he doesn't have to sit there, sip tea, and look into your eyes to while he's learning to do talk about these things. There has got to be some kind of party game that asks personal questions. You could even ask him questions about his past or inner thoughts that are light and not painful, like funny stories about his past, sexual fantasies (something he could be motivated to open up about for other reasons), or ask about his earliest memory, childhood memories from specific ages in school, or things like that. He might open up if you gave him something specific to think about.
I think you should take it easy on him about asking to open up. I wouldn't ask him to do that every day. Maybe you could mention it every so often. You wouldn't want him to think of you as the wife who thinks something is fundamentally wrong with him, something he can't fix, and may not even to be able to specifically put his finger on. Try to be content with the good you have now in your marriage, and think of the emotional issues as something that he can grow in slowly over marriage, unless he expresses an interest in working on it a lot out of a desire to improve himself. Think of this as something that you will both grow in over the decades to come. You may become adept at 'reading' him and knowing how he's feeling from subtle clues, and he may gradually open up and talk more over time. He also needs to feel like he's being accepted for who his is. He may feel like you are not please with his personality, which would be an unpleasant situation for him to deal with.