Boyfriend ex dating his best friend

My boyfriend of 3 years once was with a girl for 4/5 years they was split for 2 years then we got together. There relationship ended sour but we’ve never seen her & I’ve never met her i wouldn’t even no who she was if i walked past her. Well .... his ‘best friend’ (who wasn’t friends with when he was with his ex) he just loves to go meet girls for one thing only called & said he was messaging this girl arranged to meet and when they did she confessed that she knew who he was and explained who she was .. my boyfriends ex girlfriend!! My boyfriend isnt bothered but has said to him do what he pleases but you should no ur boundaries and thats something you don’t do! Bad on both of there parts really but hey ho.. i dunno how i feel about it? His friends always tells stories of this that and the other bird he’s been with but i don’t want him having conversations with my man about her.. the lads have all been joking saying maybe she wants him back and his getting to him this way .. Anyone been in the same situation? How did you react?

EDIT POST : the only reason it bothers me is if it got serious and she became part of our group if friends thats what i dont like. Maybe im reading into it. Just caught me off guard. I trust my man totally i just dont want to be in the same room as her & he understands that. Its my concern if her intentions are to get close to my man ..