How can friends comfort themselves when they think of their predecessors?

Criticize the shortcomings of a friend's ex-boyfriend

No matter who broke up, after all, my friend and her ex-boyfriend are very sweet, and they have a good relationship. Friends will still think of those things, and it is difficult to let go of what the other party has done. People say that after breaking up, don't say it's bad, but in order to help friends get out better, the bad guy is still a good friend, criticizing the shortcomings of his ex-boyfriend, telling some reasons for breaking up, and making friends realize that they can't completely let go of their obsession.