I saw this happen once. A friend of my fiance's lived with 5 of her best guyfriends. She got into a whirl-wind romance and got married after 3 months (they're now happily married). Anyway, they get married and her new hubby's lease ended and he ended up moving into the house with her and her 5 roommates. Though it seemed okay for awhile (new hubby fit in perfectly with her friends), the other 5 guys started to feel like the couple was isolating themselves from the rest of the roommates. Flashforward to a week ago and the newlyweds have a party at their new house (they moved out when the lease was done). NONE of her old roommates came when they all said the would! We asked the newlyweds the last time they hung out with said group and they said it was right before they moved out!

Point: you might accidentally come in between a friendship if you move in with him and his friend. I don't assume that would be your intention, but it could happen. I suggest waiting until both of your leases are up to move in together.