Time has changed. Prince Charles and Camilla married in 2005 and Wallis Simpson and David were in 1930s. Moreover, Camilla and Andrew PB are PLU(People like us) and Camilla's background is much acceptable than Wallis Simpson. It is always better for them to get married rather than just being long-time lovers but Prince Charles chooses to wait the right time.The Queen has always been know to but Duty and Country first. My understanding was that her concern on the marriage was constitutional. How would it affect the Monarchy's role and the role of the Monarchy as the head of the church of England and more importantly would Charles if he married Camilla be able to assume the throne (the ghost of Wallis Simpson and Edward the VIII) Once those issues were resolved, the engagement was announced.
Prince Charles has to clear the ostastcles before he succeeds his mother anyway.Since other heirs to the thrones have married for love, Prince Charles is entitled to the same. I think when Prince Charles succeeds the Queen, there will be no problem for them. Camilla is always a very devoted companion to Charles and she brings calm and peace to him and people will be happy to see that.