I'm going to accept my co-worker's facebook friend request and not tell my GF.
Are you serious? Why wouldn't you tell your girlfriend about it?
The girl is super cute and funny.  I like flirting with her.
It is okay to accept friend requests without your girlfriend's permission.  However, it isn't nice to flirt with other girls when yo have a girlfriend.
I guess. I'll think about it.
I think it would be okay to add friends on social media without your partner's approval. It might cause problems between you if you keep this from her. The more she knows, the better your relationship.