It's fine to talk about ex-partners in a relationship. You've both broken up with everyone you've ever been with, so it would be weird if you never mentioned anything you ever did before you met each other.
One psychologist actually thinks its a good idea to talk about previous relationships on a first date. But like with everything, there is a limit.
If your partner is obsessively bringing up their ex-partner(s), it could be a sign they are not over them, or that they are bitter about the past. It's especially important to take notice if they are being very critical about their exes.
"When people describe all of their exes as terrible people and put all the blame on them for the relationship's failure, this is a red flag for me," said Elinor Greenberg, a psychologist and author of "Borderline, Narcissistic, and Schizoid Adaptations: The Pursuit of Love, Admiration, and Safety."
"It practically shouts: 'I cannot take any responsibility for whatever went wrong. I have not learned anything from these relationships. It is totally up to you to make our relationship work.'"