so how long exactly has abby& jimmy known eachother?

Since they both grew up on the Island, I'd say they probably grew up together... Going to School and stuff. I think Abby, Nikki, Shane and Jimmy knew each other pretty well. Maybe Jimmy and Shane were a couple of years older... They would have still spent a lot of time together during High School. That's what I like to think anyway. :)

I know how in episode 12, when henry and sully were about going to shoot Jimmy, Abby noted that Henry had known Jimmy "his whole life", and 说 she had also known Henry "her whole life" (quoted from episode 13), so they probably all grew up together, because they're the same age. I liked how Henry, Abby, Jimmy, Nikki, Shane, and JD all knew each other as kids. I thought it was cool.