I don’t think it is a good idea. The ex of a guy you “used to like?” If he cheated on you, and he cheated on her will it make you feel better to know he was a dog then and still is? When people break up each person has their own perception of what happened, and maybe neither one is true. Will it make you feel better if she says he was a great guy and it was all her fault, as unlikely as that is. I just don’t see how this will do something good for you.