They know about ME?!?!??

My husband speaks with some girls behind my back and they know about me .. who i am ? I dont understand how .. One girl who always calls my husband she know about me and i dont understad does he tell them about me? Why would he? And its not his friends he dont accept friend in opposite sex ... but who are they? I just want to know your opinion about this and yes i will  talk to him about this when am ready.