The limits of honesty in a relationship

Does a real partner feel more comfortable knowing everything about their partner’s past like best friends do, do should we keep our past hidden from them? In the few relationships I’ve had in my past, my ex-partners were also like my best friends and hence I could share everything with them including my past - for it made me feel they would know me completely and also know that I am comfortable to share everything with them so no trust issues. However, my last relationship, when I did the same, I got a completely different outcome and my (quite recent) ex-partner broke up with me, saying that I’m not normal. This is strange for me because it wasn’t that I was talking about my past relationship, it is simply that I tend to have very vivid memories in general in my life and loved to tell me him everything he didn’t experience with me be it about my childhood life or family or travel and food experiences in general, and in this bunch of things were also a couple of times when I mentioned my ex, or I how at some points in time my ex made me uncomfortable over something. Nothing more. I want to understand how people’s psychology really works - would they feel more trusted and confident when their partner is able to share everything with them as a best friend or is it a strict no to talk about past relationships at all?