I think Diana was desperately craving for attention long before she married Prince Charles.
Diana was a more or less unwanted child, a girl instead of a boy and heir. I guess she felt neglected and second class. Her parents' divorce did nothing to help. She must have felt very insecure and was probably full of romantic ideas about the marriage. Diana probably dreamt of a husband that would be her knight, her 'prince', who would protect her from everything and would be just hers. Charles seemed to be the person. I doubt Diana ever loved Charles the man, but I don't think she married him for his title either. I think Diana created an image of a person and didn't see the real person behind it. But once they were married, it all changed. Diana’s failure failed to understand Charles was a Prince of the United Kingdom, that he had a job to do and that in a way, his personal life would always be second to his duty, was key to her unhappiness. Diana wanted to always be on the first place, and as a woman I can understand her. Being young and immature, she did all the wrong things. An older and more experienced woman would probably be able to mend the things, but Diana just tried to grab Charles’s attention. Her faked suicide attempt was one of those things, but it only distanced Charles (and any man would react in the same way). I do believe Charles that he turned to Camilla only after the marriage was broken beyond repair. But that probably made Diana feel even more miserable and neglected, whether she loved Charles by the time, or not. And misery turned into vindictiveness and we got the Morton book, and later the terrible panorama interview.
The tragedy of Diana & Charles, in my opinion, is that they both married not the people they thought they were. Diana married Charles because she thought the marriage would be her shelter, and Charles would be her protector, that he would always be by her side whenever she needed him (the same she later demanded from Khan). Charles married a young girl, who seemed to have the same interests as him, who, being from the same class, knew the needs and demand of the Monarchy.
Both were wrong, because Charles had a job to do, and Diana couldn't keep up with that.
I always thought, and nothing has happened to change my opinion, that Charles did love Diana, just as Diana loved Charles. But their differences and their failure to understand each other, and Diana's failure to understand Charles's position led to all those tragic events that were to happen.
Someone said in this thread a phrase that I think pretty much describes Diana: when happy, she was able to transfer happiness to the others, but when unhappy herself, the made sure everyone around her was miserable.
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