When getting into a new relationship, did yous talk or anything about your past?

This is my first relationship with a guy I haven’t gone to school with or knew well beforehand so I know nothing about his past but he knows about my ex

Like I don’t wanna know about his ex’s because I get hella jealous sometimes. but I’m sorta curious about when his last relationship was

And I get curious if I hear of someone and his mates like laugh or something. Like is she an ex? Why is it funny? What’s the inside joke ?