Diana loved him
I think Diana at 19 loved the idea of him and the idea of being PoW.
Realistically, they had only met a handful of times before getting engaged. I very much much doubt either of them knew each other enough well enough to be in love.
Unlike yourself I do have some sympathy for Charles and the pressure he was under to marry (and marry someone "suitable").
I believe it's too simplistic to say he was the villain here.
Upshot is their relationship was a disaster and I think both of them were failed by people around them who should have been more supportive in them both putting the brakes on.
I will also admit to liking Camilla and think she's proven her worth, especially with her work to highlight domestic violence.
Fundamentally, I can't fathom the vitriol against a couple for events that happened decades ago and when the perceived injustice was against a person who was far from perfect herself and caused considerable hurt to others with her multiple affairs.