Some people have an ex-boyfriend/girlfriend/husband/wife that was very troublesome in their past relationship together. Perhaps they were cheaters. Maybe the were physically, emotionally, and/or psychologically abusive. They may have been neglectful or even possessed a personality disorder. Many exes are exes for a reason: because they have notable problems that led to or at least contributed to the demise of your previous relationship together. However that relationship ended, perhaps you can just give a sigh of relief that that person is no longer in your life. Hopefully now you can just move on and choose better in the next relationship.
On the other hand, letting go and moving on from such relationships can be challenging for many reasons. One factor that often can keep someone tied to their troublesome ex is the temptation to want to warn the new person they are starting to see (or someone who is considering starting to see your ex) about all of the terrible traits and tendencies of the ex. You may tell yourself that warning the new person is just “the right thing to do”. Or you may tell yourself that “I wish someone would have told me about their problems earlier on, so I am going to give someone else the favor I never got”. There are many rationalizations and justifications to warn a new person about the problems with the ex. So, should you?
When Warning Others is a Bad Idea:
In my opinion, after having working with such scenarios in a therapy context over the years, I would usually say no. The ensuing problems generally outweigh the benefits. It is usually not a good idea to warn the new person in the life of your ex about all of their problems and issues.
Read about why warning others is a bad idea here!