IMHO there should be a separation between your job and any personal activities.
TO single out one passenger for attention over others is bad work behavior. IT's like working in an office where some employees can get away with everything while another is singled out for criticism. (trust me it happens on my job.)
F-A's can be friendly. I have had F-A's who stop and chat with me on everything from my travels to my cats to Jimmy Buffett. But I am always careful to stop the conversation if I sense another passenger is getting annoyed (I have good cat sense about people's emotions, most of the time.)
If one of my familar angels is on a flight I'll wait till after meal/drink service and go to the galley to chat.
I don't want an F-A to get into trouble.