I`m pretty much sure that Charles and Diana would have faced similar problems if there hadn`t been Camilla in their marriage. Diana said that their marriage was too "crowded" but this is not the only reason for the failure of their marriage. I think that they were destined to face huge problems in their union. It is dificult to find two more mismatched people that were to marry.
Princess Diana came from a broken family. She confessed of her lack of security and stability. She had to listen (probably) to her parents` quarrels and see her mother weeping. The Spencer children had to spend their lives in both parents` houses no wonder that she felt so unhappy and insecure. I don`t know how much this situation affected Diana`s siblings but Diana was very much affected. In fact, she became emotionally fragile having problems with passsing her exams at boarding school. I wonder if she even had secondary education? A very unhappy girl dreams of the Prince Charming who will one day come and rescue her. This man will fall in love with her and give her his unconditional love. This is what she needs and this is what she will demand from him. Her craving for love and affection was really enormous, in my opinion. Besides, she wanted to love someone and being loved in return. the more unloved she felt the more love she needed. Plus, she was a very emotional and sensitive child who turned into a very emotional and psychologically insecure woman.
Prince Charles grew up in a seemingly "normal" family. But can the Queen`s family be called "normal"? Charles`s mother was preoccupied with her duties as a a Sovereign as duty was always uppermost in her mind. He saw her only from time to time and I doubt whether he could spend time with her like other kids could i.e. go for a walk, listen to a fairy-tale etc. The Duke of Edinburgh was a very emotionally cold and demanding husband. Charles was not his favorite son, he preferred Anna to his sons. Charles publicly admitted that he grew up in a very cold atmosphere, that he experienced no approval from his parents. The Duke of Edinburgh wanted to make Charles an emotionally and physically strong statesman and soldier but Charles seemed to be more of the "artist" type. No wonder that Charles felt misunderstood and under appreciated. Due to the lack of unconditional love and approval in his childhood, Charles needed to be loved. approved, reassured, pampered, praised etc. He needed someone that he could emmotionally rely on. And this person was Camilla, to some extent a mother figure.
Charles and Diana were mismatched from the very beginning. Two emotionally unstable people craving for love and affection and acceptance. No one cared whether these two would suit each other. Diana finally found her Prince Charming, probably she even loved him. Though 13 years her senior, Charles was so immature that he wasn`t aware of the possible problems that might arise from such a match.
Were they doomed to failure? Mmost probably yes though some people who turned to psychotherapists managed to improve their marriages because they worked hard on it. Psychtherapy helps one to get to know oneself : one`s needs, inner probles, the source of these problems. But I don`t thoink that anyone in the Buckingham palace has ever imagined that Charles and Diana would have visited a psychotherapist! Diana was regarded to be emotionally unstable, Charles foun a "psychotherapist" in Camilla.