Low-down dirty shames

I am married and my husband has a stepdaughter by his first wife and a bilogical daughter by his first wife also. I am really having a problem with his stepdaughter calling him early in the mornings and late at night leaving him messages about how she really misses him and really love him. She also asks him not to leave her and tells him when she is on her monthly. I confronted him and asked what is going on and he says that she always call him and it is okay for her to say the things that she says. She is a 44 year old woman and claims he is the only one that consoles her when she is depressed. What do you think about this situation? I told him to get to stepping. Am I wrong?