Husband obsessed with past

Been with hubby for 20 yrs and have a really healthy sex life but for the past year he’s been obsessed with knowing all the sexual things I did before being with him. Not from jealousy but as a kink (I think it turns him on). The problem is that it gets on my nerves because first of all, I don’t remember everything since it was such a long time ago, second of all I am not the same person and I don’t really care about the past and exes like he does. When he ask questions and my answers aren’t really clear he gets upset and says I don’t want to talk about it which is true because I don’t see the point! I don’t care to know what he did before me, why is he now so obsessed with knowing details about what I did before him all of a sudden???