Jacob feels less loved that MIB, agrees to stay with Mother

As Mother sits on the beach alone and Jacob joins her. Jacbo asks her if she thinks the Man In Black will come back, and she says no. When Jacob asks if it's true that she killed his real mother, she says yes. Mother explains that she killed Claudia so that she wouldn't take Jacob back to her people because they are bad and would have made him bad too.

Mother adds that she needs Jacob to stay good. Jacob asks "Am I good, Mother?" and she tells him yes. He then asks why she loves MIB more than him. She says that she loves them in different ways and then asks if she will stay with him. Jacob says yes, but as she leans on his shoulder, he adds "For a while."

So why is it that Mother doesn't love both of her "sons" the same? What made MIB more important, or special than Jacob? This was certainly a tense scene where it becomes clear that Mother is more concerned with the well-being of her own agenda rather than the well-being of her "sons."