HELP, my tenant is bring her boyfriend over every single night

[Garle Io]

My tenant has been bringing her boyfriend over every night for almost 3 months now. We pay for internet, garbage, except for water & electricity. We split the utilities by the amount of people in the house (her, me and my parents). She lives in the rear part of the house with a separate door, located in daly city, CA. Now the bf had been coming and leaving with her every single day.

Before and on the day she signed, we talked about this topic. We briefly agreed that her mom can visit her for 2 months as long as she pays for her share of the utilities too. We agreed that occasional guests visits for a few days are fine without paying extra, but if any visits for a longer period of time like weeks and months that she should let us know in advance and we can divide the electricity bill accordingly. Our ad stated that rent would be at this different amount if for 2 renters. My lease only says "The Premises are for the sole used as a personal residence by the follow person only."

He's not a guest to me anymore, more like a roommate who lives here. Is it fair to explain to her that a regular guest should only be staying 1 or 2 nights a week? Otherwise we are willing to add him on the contract with additional rent.? Please help....