I think my ex-boyfriend thinks I'm dead
Why do you think that?
He never talks to me or acknowledges me when he sees me.
I don't know how bad your breakup was, but that can be hard for either of you to get over. You should probably just give him space.
Do you think he hates me? I really wish he'd just tell me I'm dead to him or that I hurt him too badly to be friends right now.
It's possible that he just wants to move on, however, if this is really bothering you, you can reach out to him one more time.  Just let him know that you are worried about him, and he will probably respond, even curtly, to let you know how he feels.  If he says that he's fine, then he probably just wants to be left alone, and it is not your fault.