He refuses to change his ways

I have been married for over a decade. My husband and I are both in our late forties and have settled into a stage where we know this is what the rest of our lives will be like. We have no children and are financially stable. The problem I have is his refusal to change who he is as a person. There are some behavioural characteristics that have only become worse with age, and I am pretty sure he is not interested in doing anything to address them. I try and evolve as a person, but he is stubborn and won’t listen to anyone when it comes to his beliefs, which makes me sad because I know he will end up being a bitter person. Is it possible for someone like him to change for the better at this point? 
Everything is possible if one is motivated enough to try and become a better version of themselves. Stubbornness is hard to address, but love and patience can make a difference, especially if you can communicate why this matters to you as much as it clearly does. Your husband may not be able to change everything about himself, but the first thing to focus on and address is a willingness to open up because that is where half the battle lies. If he can talk about how he feels, and why he does the things he does, he may be able to acknowledge what you are saying. Try working on how you communicate with each other, don’t be afraid to be vulnerable, and talk about growing old together. Don’t give up.

The man I am dating doesn’t want his friends to know about me. Is this a red flag?
If he has no explanation, or one that isn’t reasonable enough, it is definitely a red flag because you are entitled to be accepted as part of his life. He owes you that respect. If this continues without any resolution, you should ask yourself some difficult questions about this relationship.