[RT Wolf]

Occasionally, overprotective mothers will use emotional blackmail to exert power over others, especially their kids, and sometimes those kids learn those techniques and then use them against others.

So, while its possible that she's made you the center of her life, become dependant and can't handle the thought of you leaving (which has, again, nothing to do with you specifically, any other person in your situation would probably arouse the same reaction), it is also possible she is using that as an unconscious ploy to keep you around. Consider carefully. The way to tell if its a "Games That People Play" (good book) is if you say you're leaving anyway and she reacts with anger. This is a high risk test, though, so you might wanna just think about it otherwise.