I secretly don't want my ex bestfriend and her ex beau to get back together. He is a gem of a person. She is plain toxic.
How come you do not want them to get back together?
Because their relationship will not last long.
If they want to get back together, that is their choice. You do not get to decide what they do with their lives.
She will break his heart. That is what worries me most.
Whatever the case with them, be more logical. It is not your place to try to get in between anyone's love lives no matter what your thoughts are about it, it will only make matters worse.