Never talk about past partners.

No one needs memories of past partners, they can only interfere and hurt. You should not talk about them even in passing, and even more so in detail or expressing regret or admiration. It's one thing to theoretically know that someone was, and another thing when they talk about it directly, and even express emotions. There are people who think that by learning or talking about previous relationships, they insure themselves and their partner against repeating the mistakes of the past. But it doesn't work that way. Old experience will not help, but only hinder.