Can non greek guys go to formals?

[evorevo]

May seem like a silly question. Anyway I'm a guy not involved in Greek Life. I am dating a girl and can see it progressing. She's accepting her bid in a sorority at my large state school in the spring. So question is, can a guy go to a formal even if they aren't in a fraternity? Is that common? Also would you say that girls in sororities usually add their sisters as a new group of friends or replace their friends?

Thanks