I learned very quickly who I can trust and who I can't. The nurse who trained me isn't all that older than I am so we're pretty close at work, but not so much outside. I have several close friends that I've been friends with since elementary school, so I never feel like I'm missing something. I go to work, I socialize, then I leave it there. We also have a couple people who are widely known to be backstabbers and you never discuss anything with them beyond "can you waste some ____ with me?"
I have an interview tomorrow for a new job and I'm pretty sure if I get it, I won't keep in contact with people at my current job, and I'm ok with that.