The closest word I can think of is a sycophant but that's too strong word and not exactly what I'm looking for. The word I'm thinking of has negative connotations and it's for someone who is friends with different groups but only at a superficial level and isn't necessarily honest about who all they're friends with. This person would be seen as untrustworthy.
Such a weird concept - you don't trust someone who has a wide variety of friends? I have several very different hobbies/activities, so naturally there's little overlap in my friend groups. Most of my friends are like this - for example one belongs to three choirs and I don't know any of those friends. Or her kayaking friends, or her work friends. I'm giggling thinking how baffled she'd be if I started questioning her "loyalty". Even my very closest friends have other friend groups I'm not part of. So what?