Tenants boyfriend over every day, laws on this?

[Ian Loonce]

A tenant has her boyfriend over everyday, most likely staying the night.  The car is always there.

It's been there every day for 2 months since she moved in.  He technically has is own dorm room at the university.

Our lease says no one else can live there but it doesn't say how long guests can stay.  I'm wondering what laws there are in Ohio and what can be done.