Hello, In happy, lot of sex relationship, about 7 months. Met with her friends, next day her friend texted her "hes cool, much better than "X"

We never talked about exes, so I didnt know, however i ocassionally see X on her fb messenger, shes not hiding it and it seems more like casual conversation.

How do I aproach this? Should I tell her I dont accept texting or talking with ex ? How to do it without seeming like butthurt kid?

Thanks