Groups of friends kept seperate?

Alright so I've got like, several groups of friends, some are just one person but let's consider them groups. is it normal to always be like, juggling them and trying to keep them separate? Like, I have this one friend who is like a total loner. I am pretty much his only friend. But instead of introducing him to my other friends I only ever hang out with him. I've tried introducing him to other friends and stuff but I usually end up feeling embarrassed and he kind of ruins the fun a bit. Then there will be a girl who I hang out with sometimes but who I don't want to introduce to my other friends because she is so different. I feel like they could probably get along but then we'd all start hanging out together and I would feel like something had been lost, because I like hanging out with her to get away from my other friends.

I actively try to keep my groups of friends apart, and it makes me feel manipulative and possessive. Is this normal??