Haha! You have more persistence than I do. I just looked around and was like "Screw it." Log out. New world. Bam! I still kept it though just for giggles. Maybe I should go see how long it takes to get to mainland. Have you gone back to the island via boat and gone in the other direction to see how long it is that way?
If I would just be so lucky! I haven't seen a diamond in the whole game!...It's can maybe be 'caused by a several bugging programs that I need to delete. But still... When you found that cave, how many monsters did you have to slave? I tried to mine to a lava level ones and found a huge cave! there wasn't much than stone around... There was some lava thought but I didn't want to risk my life to go down 'cause down there was huge punch of all monsters from skeletons all the way to enderman. And I know that when there is more than one enderman... You better back down for a while and come back later... Do you have a good advice how to defend yourself the best from the monsters? From my world I haven't found much any iron so I have been able to do only leather armor to defend myself.