I think a lot of girls go through what you're feeling now, including myself.

I took alumna status early at 22 as I became a 5th year senior. By that time, most of the sisters that I was very close to were already alumnae and no longer in the chapter. I had one pledge sister left, but I felt like I didn't have a lot in common with my younger, 18/19 year old sisters.

After a while I wouldn't hang out with my sisters as much and I'd see them only at chapter and the mandatory events. I wasn't mad at them and to this day I still care for them, it's just that after a while you develop other interests and you prefer hanging out with friends outside the sorority.