First off, I don't pretend to be a writer or a word smith of the written language, so bare with me.
I have watched "Across The Sea" over and over again and can't get over how much MIB and Jacob cared and loved each other.
Starting from little kids even until going their seperate paths, they always cared.
I think Jacob is tragically flawed. He is consumed by his obligation to protect the island and treasures life to the highest degree. I think he was in fact afraid of death, something the MIB never seemed to fear.
We have seen MIB on 1 accont say to Jacob "Do you know how badly I want to kill you right now" and personally I don't interpret that the same way as most.
MIB killed his "fake" mother in cold blood. He was in a rage. Yet he was still perisistant on bringing Jacob with him and escaping the island, he wanted the 2 to go together.
I think when MIB said he wanted to kill Jacob, he was somehow aware it would bring "both" of them closer to escaping the island, and in fact being together.
I think that there is going to be a very "ah ha..." moment next episode, especially regarding MIB real reason for most of his actions. I think there might be some validity to "the greater good" and he may actually be looking out for his brother best interest.
I just think what is said may not be what it seems, but hey this is Lost...