Every relationship is different. I do suffer from jealousy, mostly due to insecurity issues. I sometimes find when my boyfriend, S, is sharing details about his time with his other girl, J, I can feel this jealousy and insecurity rising. At that point I like to ask for some reassurances and that helps a lot. And ultimately I like that S can share things with me. I feel worse if I think he's holding things back from me.
When it comes to sex part and their own private conversations that is their thing. He will update me if they have a chat about where their relationship is. With the sex, we've agreed on safe sex practices and I trust he does that. I know how often they do it but no other details, I personally wouldn't mind knowing more about what they get up to in the bedroom, but J prefers to keep that private, so I respect that is her decision.
I would say you should talk to your girlfriend about what you want to know, ye can set up boundaries of what is comfortable for everyone involved. Also if you find hearing the details is actually hard for you, I would advise you not to be afraid to ask for reassurances or to redefine what you want to know, you may need to take it step by step.