Someone new living with tenant

[Jake Whisler]

My tenant has someone who is over all the time. I believe it is her boyfriend. She is the only one on the lease and no one was ever over there for the first few months. He has been there almost every day for the past 2 months as well as being there even when she is not there. Is there any law about him being there without her there? Should I have him added to the lease?