Should i worry?

ok so my boyfriend of three months is wanting him and his brother to share a duplex with one of his friends the problem is the friend he's wanting to share the duplex with set him up with a girl right before we started dating he liked this girl alot but decited he didn't need the kinda stuff she was into in his life... the girl is like best friends with my boyfriends friend i know this sounds confusing...sorry...anyway if they share the duplex she will be over there all the time... i don;t trust her.. should i worry?