we bring about our own anxiety and illness and stress
We do, for sure, but it's not an easy thing to recognise or fix. Often our instincts can completely turn against us in this regard.
Yes, for a long time I couldn't understand people forgiving others for things like that. You can't change what's happened, though, so at some point you have to make a choice between allowing it to destroy you or healing from it. Ultimately it's not even about them and they will probably never know whether you forgive them or not.