I think it takes two to make or break a marriage. I don't think Charles was the main reason the marriage failed but I don't believe Diana was either.
I don't think Charles was used to compromise in his private life. As an adult he had been used to getting his own way, people agreeing with his pronouncements on life, having people rushing to anticipate his wishes, aides doing his research, a large number of servants and other staff making his life comfortable and easy.
He expected a very young woman to fit in with this, and, like his staff, anticipate his wishes and make him happy, perform the role of Princess of Wales and share his hobbies and interests. What about her hobbies and interests? Did they not count? What about him thinking about anticipating her wishes, (developing an interest in modern music for example) adopting a few of her interests in their future life together? Apparently that wasn't expected to be important.
What young woman would be happy and satisfied with the man they're engaged to sitting them down and saying "Well, I really don't love you in the same way as you seem to love me, and I don't love you as much! However, I want us to share our interests and I am sure that I will learn to love you after marriage. I am sure love will come on my part...." ?? Most young women, let alone 19/20 year olds would be absolutely devastated at those sort of revelations. In fact, I think most women of any age would walk out after a conversation on those lines!
I think Diana was in love with Charles, yes with the whole shebang around him, but with the man too. I don't think that too many 19yearolds in Western societies anticipate marriage without romantic love, stars bursting in the heavens, hearts churning, the feeling you'd do anything for the loved one. The sort of love in fact that Charles obviously felt and feels for Mrs Parker Bowles.
In that, I believe that Diana was absolutely typical of her contemporaries. And I tell you what, I was 27 when I got engaged and I wanted and expected and got that too.