Inkigayo has released the official videos of SISTAR’s final 2 stages from the June 5th episode, including a hits medley featuring “Shake It,” “I Swear,” & “Touch My Body” as well as their current, final song “Lonely.”
I know that Aron and f(x)’s Amber are very close (he even appeared in her Shake That Brass MV) and I believe Minhyun has a few friends in other K-pop groups that he went to school with (the Boyfriend twins, for starters, who graduated the same year as him). Ren also seems to have a few connections here and there (he’s often seen posing in other idols’ instagram photos).
For the most part, however, the boys really only hang out and talk with each other or other Pledis artists. Minhyun is very close with Mingyu, actually. I think most of NU’EST, outside of Aron, are relatively introverted or prefer the company of a small group of close friends. For a long time, they didn’t really branch out and talk to other idols, but that’s another reason why them going on Produce 101 has been so good. It allows them to make friends with other people in the industry, and connections can be vital in this business.