My question involves an eviction in the state of: New York, Queens

My ex-girlfriend who currently resides in my apartment won't leave the premises and brings her lovers and unknown guests into my apartment.
I'm am the sole-person on the lease.
She has lived here for about 2 months.
She has a room that I let her stay in with privacy.
We've spoken with police officers twice.
Once the officers said she wasn't the lease holder therefore she wasn't allowed to bring guests in unless I allowed, given the privacy issues and endangerment.
The second time officers said she could bring in anybody she wanted because after 30 days she becomes a tenant.

I'm very confused and feel they are completely wrong because If someone is doing something to endanger someones health purposely and provoking some physical behavior out of the other shouldn't that be deemed wrong.

Then since the heat has been scorching here lately. I want to install and A/C and we live in a railroad apartment (connecting bedrooms, seperated by a door) and foolishly i gave her the bedroom with the windows and now I want to open the door so I can benefit from the A/C. Is that illegal to enter one of my bedrooms that she stays in? this whole process is driving me insane and the police can't seem to do anything about it. I'm contacting the landlord tenant courthouse in a few hours but i hope you can give me a few pointers and make sense out of this situation. It can cause a lot of animosity. thank you