Although none of us know what really happened in the marriage, I think Charles went into it wanting it to work, but very soon it was patently obvious they had nothing in common except a shared love for their children.
The age difference, their totally different interests, just their whole approach to life, - with hindsight, absolutely doomed.
I honestly think Camilla is his soul mate, and has been so good for him. The way William and Harry are with her shows that they think so too. At least, that is how it appears to me anyway.