Is he so incognito about cheating on me?

i need some advice. i am dating someone who has moved to a different city recently; with his bestfriend and his best friends girlfriend. i am planning on moving in very very soon with all of them. i need to know if this is a good idea, because it seems as if my boyfriend is cheating on me with his best friends girl. shes told me that her boyfriend and her have been having problems and now that my boyfriends around, its like a breath of fresh air. its been two months now since they have all lived together–her boyfriend works the nightshift– and since my boyfriend works with his girlfriend, they have ALOT of time to spend together– they even both get off of work at the same time. since i still live in a different city, how am i supposed to know whats going on with them. she bosses him around and he seems to enjoy it– if not welcoming it himself. and every time im around, he only wants to go to work to hang out with her. it seems as if im a nuisance and it seems pointless to be over there with him because all he talks about is her it seems. im not overexagerating or overanalyzing. he even had the nerve to ask me for a few dollars because he wanted to get her something to eat. she even does his laundry. and since the both of us almost have the same name, he calls her by my nickname– please help me– am i in denial???