Did Charles always love camilla even when he was married to Diana?

No.

For one thing, he was already secretly committed to Camilla as the love of his life.

For another, he didn't actually choose Diana. He was pushed into it by Prince Philip, who thought there ought to be a glamorous young Princess, who could bring some good looks into the royal bloodline.

Even a glance at the two of them together shows that there was no real rapport. He was hopelessly wrong for her. But she was too young to know what she was getting (pushed) into.