Friends with an Ex???

Okay long story short my boyfriend told me that he is good friends with an ex of his. Him and this girl dated for 5 years and lived together for 3 of those years. I personally believe that you can’t remain friends with an ex unless you still love them or you never did love them. Well we went over her house so I can meet her and she said something about him and he replied with his cute little flirty voice. She does now have a kid with someone and lives in a different state. I just wanna know if I’m overreacting about this situation or not.