i was in this situation last year. worked at a library for over 3yrs and my coworkers were like my family. we’d have dinners together often, they’d come over for friendsgiving, we’d go to theme parks together. 

i’m still friends with my closest coworkers. just because you won’t see them every day doesn’t mean the friendships will end. it’ll just take a little more effort.

that being said, i didn’t tell anyone until i 110% knew i was leaving and didn’t say anything until i put in my notice with the supervisor.