Tenants boyfriend is not on lease and may have moved in.

[Leroy Wallace Jr]

I have a duplex, owner occupied. 

First and foremost, my Tenant is awesome. Pays his rent a day early and is very respectful. His kids live with him (they are 27 and up). They moved in in June and everything has been great.  His daughters boyfriend has been hanging around ALOT, and I believe he has tried to secretly move in.  I did tell the boyfriend a couple of weeks ago that if he is going to be living here that he would need to fill out an application and background check.  He said, "I just be stayin here alot."  To which I replied, "If you are going to be living here I need you on the lease for legal reasons."

Fast forward to today.  I get home and I have mail for him in my mailbox from the RMV.  My tenants daughter and him both sit out in the car and smoke what feels like all day.  I don't say anything about it since I would rather them do it outside than in the house.  Figured I would pick my battles.  He does some stuff thats annoying, and I have to tell him to not do it (ie. work on his car in my driveway).  They also have begun to fight.

After seeing that he received mail here I reached out to my tenant and told him that per the lease agreement anyone that is not on the lease is not to be living here, and that if he would like to amend the lease we can do an application and a background check and go from there.  I am waiting to hear back from him, this has all only happened in the last 2 hours or so.  

In my lease I have it written into my lease that "Any unauthorized occupancy is considered illegal occupancy, and the landlord will have the right to end the lease with 30 days written notice.  An unauthorized tenant is one who is not on the lease."

However, I don't want him to live here, but I also don't want to lose a good tenant because of the boyfriend.  I have googled his name, and (2) minor arrests show up for driving on a suspended license.

Any advice?? What should I do?

Thank you in advance!

Leroy