Tenant seems to have immediately moved GF in, despite only him being on lease

[Jack B.]

This is a MIL apartment below me, in my house. I prefer not to rent to couples due to the extra traffic, noise, etc. As it stands, she has been here EVERY DAY since he moved in Friday and she appears to work from home. 

It bothers me, and I'm considering telling him I don't like it and giving him notice or asking about it. He is a 21 year old kid that just became a Cop. It's already been an issue because I only have three parking spots and they took up two, and I had to tell them the extra spot is for my guests, they can park down the street. I don't want MY GF walking from down the street to my house while they immediately take up all the parking. 

Ultimately I think he might be a bad fit because he doesn't seem to understand these things, he just moved out of his parents house.

I might just tell him my GF is moving in and have him move out in a couple months, or should I just try to adjust to this as uncomfortable as it makes me? AGAIN, he never made any mention of anyone else moving in with him. I asked about it and he said his GF might be over occasionally but so far she has been here all day every day with him and when he left for work today she stayed behind so I assume she works from home, which I also don't like, having tenants here around the clock. I rent this place out at 50% of market value and prefer people who are more quiet and work a normal office job.