Friends with your exes.

Is it OK to still be friends with you exes. I'm not friends with any of mine but my boyfriend told me he's friends with all of his. I met one of his yesterday. She was pretty cool just idk she kind of overstepped I think. We were in a restaurant and she was sitting there basically acting like she knew everything about him, telling the waitress to make sure she does this or that for him and I'm just sitting there like me name dim have been together longer than yall were. It made me feel like I didn't know as much about him as I thought I did. I understand they dated but me and him are together now. I don't really have a problem with it just they had something in the past and sometimes that just makes me nervous. I know I'm probably over thinking. What are yalls opinions?