I need more freedom from some friends at school. how?

[sky]

I wasnt in the more unpopular group at school a few years ago, but since i went into highschool i have merged into a more unpopular group. I am still friends with the popular group at school but i dont hang out with them. One of my more unpopular friends is very mature and if i dont meet him after school or at lunch i will get a huge lecture. me and my other friends agree that he can be a bit stricked and i have had enough. i dont want to be mean to him but how do i get out of this group without telling him that he is annoying or mean?! please help if u understand.