I just tell everyone that Mono is my friend and that he lives with us. I took the lead from LB actually, our son, he did a "about my life" project for school and added Mono's picture to the project... people asked who he is and he just said, "he is my best buddy that lives with us"... there was some confusion but people took it in and accepted it as LB's normal life, much like anyone else's family is normal to them. Mono goes to school functions, picks LB up sometimes... no one gives him a second glance really. Or maybe I just shrug it off as not their business and them looking for gossip.
Really, its all in the confidence and the normalcy of the presentation. It really isn't anyone's business until you decide to make yourself vulnerable by talking about it openly.
It's early days for you two. I would think that your partner is not about to want to invite the new love over for a family reunion or anything anyway. When big family events come up, or holidays, if the relationship has reached the kind of depth that requires it, it can be important to negotiate who spends what time where and for how long.... but, its early yet... so some "waiting to see" is in order first I think.