I agree, but I don't think that means that - before 1986 - he was cheating on her with Camilla. The omnipresence of Camilla was a Diana invention "there were three of us in that marriage" being a very good line and more catchy than giving the real numbers from both sides.
I suspect she said it as a way of gathering public support to herself in the War of the Wales, and of course it's always easier to damn the OW (which she was by time of interview) than blame the man, or shoulder your share. And of course, though I doubt very much this was her intent, it was later used in the "thwarted true love" revisionist narrative to make Camilla acceptable as Queen. That worked brilliantly
If it is correct that Charles did not have affairs in the early part of his marriage, resuming in 1986 (whether that was with Camilla or others) then yes, he was waiting for her to do something that gave him permission. 1986 saw the end of the affair (possibly emotional, not physical, but admitted to by Diana as highly inappropriate) with Barry Manakee and the the start of her relationship with James Hewitt.
It seems that Charles was not going to do anything about his wife's affairs (as long as she did not publicly embarrass The Firm) but if she was having life on the side, so would he.
How far each is responsible for the state of the marriage before 1984 (start of Diana's affair with Manakee) can only be guessed at. But looking at threads on ordinary people having affairs , the advice is always that cheating is not the answer, that if something is wrong in your marriage you fix it or move on, you don't betray; or, if you were the cheated on party, it's not about you it's about the character of the betrayer. And the then Wales were a mess - in both directions it seems