Hmmm. I think it lacks a bit of information on whether this current girlfriend complains about this, or all his past girlfriends... and a bit of a decision making wrt how they want to handle the questions the girlfriend asks (there's a few question marks in there suggesting possible ways of replying, but they kinda need to pick one).
It's also not really clear to me if it's about honestly answering those questions or, like the top answer takes it, in general talking with the girlfriend about exes.