I don’t feel sorry for the mistress. And I don't think she loved the man as she claimed. If she did she would have protected the man's secret. The widow didn't have to find out.

She just wanted to rub off the man's betrayal to his widow. She could have quietly attended the ceremony without introducing herself or go after the funeral. But no, she exposed the man's secret, maybe as payback.

If the man loved her as much as she did, he would have divorced his wife for her. For 5 years they dated the man still choose his family. I'm guessing she had ulterior motives for telling the widow about the affair.