How do I get away from the mother role with my friends?

In my relationships with all my friends I always end up playing the mother role. I'm always the one they come to with all their problems. I'm the one people come to when they have problems with one of my friends. And the one they always look to keep them from doing wrong. Don't get me wrong. I am flattered they think enough of me to trust my judgement. But it's gotten to the point that they think I should be involved in every aspect of their lives. If they want to go out and do something and I don't, they won't go simply because I won't go. And what bothers me most is that they sometimes do things and try to hide them from me because they are affraid of what I will think. Things that friends should tell each other. But when they tell me things and I don't offer my opion they nag me until I tell them if I think they are wrong or not. How do I get them to look at me as their girlfriend again and not want me to mother their lives?