Bf friend

Hi guys so my boyfriend used to talk to this girl that I know before I got in the picture n I didn’t find out until we started talking. I came to the realization recently that they still keep in contact n they used to talk the end of last year n we met in February. I expressed to him how uncomfortable the situation makes me feel but they are still in contact. What should I do in this situation? Btw, my “friend” never told me anything my boyfriend did.