Without having all of the facts it is important to realize that you have come to a very premature and irrational conclusion. This early conclusion is probably based on your fear of being abandoned as you mentioned. It does seem as though you have overreacted to this situation and I say this precisely because you have jumped to a conclusion without knowing her motive for leaving. The bottom line is that you have not learned why your mother wants to move. Until you have the facts, it is impossible for you to draw a reasonable and informed conclusion regarding this matter.
While it may feel like your mother is abandoning you there could be a very logical explanation for why she is leaving and moving to Kansas. Conversely, it is equally possible that she does not have a good reason for moving but her reason for moving, whether it is a good reason or a not-so-good reason, likely has nothing to do with something that you did wrong. Nothing in your letter indicates that you have something to be guilty about. A feeling of guilt implies that you have done something to feel guilty about. You mentioned that you have a mental illness but please know that having a mental illness is not something to feel guilty about.
The key to finding out why she is moving is to ask her. You can say something like the following: “Mom, I love you and I am very much attached to you and I am confused, saddened, and concerned to hear that you are moving. I feel a strong connection and bond with you and when you said you were leaving I had an unshakable feeling that you were abandoning me. I am wondering why you are moving, and why so abruptly, without discussing it with me and without my input and feedback. I need you to explain to me why it is that you are moving.”
You have every right to ask your mother why she is moving and you have every right to receive an answer to this question. Communicate with your mother about your feelings and find out the truth. Doing so might not change her mind but it may put to rest some of your irrational fears. Good luck.