What will happen after I text my landlord about my sisters boyfriend?
A lease is a contract. Its not the law. Its an agreement between the landlord and those who signed to abide by the terms of the agreement. As mentioned in earlier comments, much depends on the laws in your jurisdiction, the landlord, and the other lessors. But in most cases you always run the risk that the landlord may terminate your contract for changing the terms unilaterally. Although I stand to be corrected, three is a crowd. It sounds like somebody is going to have to move in the near future. Maybe in a calmer moment, when the boyfriend isnt around, it would be good to have a calm chat with your sister about this, and where its all going. If she doesnt have any plans, and wants to keep things as they are, you yourself may need to make plans. Crappy, but it happens all the time. Cheers!