Can a landlord raise the rent if he suspects someone else living there?

Ok, so me and my friend got an apartment together, because my boyfriend got a job where he will be traveling during the week, and only home on the weekends. So anyways, *me* and *her* signed the lease for our 2 bedroom apartment. Since the day we moved in, her boyfriend has been there. He sleeps over every night... show more Ok, so me and my friend got an apartment together, because my boyfriend got a job where he will be traveling during the week, and only home on the weekends. So anyways, *me* and *her* signed the lease for our 2 bedroom apartment. Since the day we moved in, her boyfriend has been there. He sleeps over every night and is there pretty much all day until he decides to go into work. He has random belongs there (his tv in the livingroom, his X box, shower stuff) but it's not like he's 100% living there. Anyways, our landlord lives literally right down the road and is always at our place fixing things, mowing the lawn, etc. I was under the impression that if he keeps seeing this 3rd car there, and has reason to believe there is a 3rd person there, he can raise the rent. My roomate says because the lease was already signed for the monthly amount, he cannot raise it. She said because the lease didn't say on it that he potentially can raise the rent as long as he gives us a 30 day notice.. then he cannot do so. Is this true?
Update: Just a p.s., this is for the State of NY if that matters at all..
Update 2: Our rent included all utilities (obviously minus cable/internet)
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