Even though Queen knew about Charles's loose pants why did she not support Diana?

I'd suggest because Diana had by that time, become just an embarrassment. Courting the media? Encouraging a celeb. status? Hardly how any royal should have been behaving!! Like it or not, Diana was a lose canon towards the end of that marriage which apart from providing the country with the needed heir and spare, should basically never have happened. It was a partnership that was doomed from the very beginning.

And where is your proof positive that Charles has having multiple affairs!!!! Not that throughout history did royal males NOT have mistresses!! Something Diana might well have been wise to have realised instead of thinking she was marrying into some fairytale story.

Perhaps because Dianas pants were much looser.

Because he is her son and the next king.

She just didn't like Diana at all. Diana was marrying a muslim man. She was an embarrassment to the RF