Sounds like her father's illness may have been a "starting" trigger for her. She saw her father in a different light when he was sick.
As for her changing her mind about the divorce...not surprised. She doesn't want to spend the money on a piece of paper when she can continue to live as she is at the moment and that you will go along w/it because of the $$$ to get a divorce.
You do not know whether she'll get through her crisis or stay stuck, so the word "never" is a bit premature because none us know what the future will hold for her.
Please take some time to digest the info you received. Do not make any decisions while you are upset and/or angry. Usually those decisions will come back to bite you. You want to make decisions when you are calmer and have investigated all angles as to what you need to do. You have a decision to make: 1) stay in the home and live w/her and her behavior 24/7 or 2) find a new place to live which will provide you w/peace and a place where you can go to think and begin moving forward w/your life. However, before you do anything, please consult w/a lawyer to see what your rights are. You do not want to be labeled as "abandoning your home and family". Be sure to take care of your checking/savings and credit card accounts, i.e., remove her name from them. If she is in crisis, she will begin spending more money and not care whether you and your child have everything you need. If you must support her financially, set up a separate account and have funds put in electronically so that you have a record of the deposits being made. Some of these crisis people will swear you didn't give them the money, i.e., their memories become mush the longer they go on. You need to protect yourself financially. Seeing a lawyer will help you in setting up a visitation schedule w/your child, as well as to advise you of what you will need to provide in the way of support funds...again, it's important that this financial arrangement be documented.
It sounds like you are thinking of cutting your losses, i.e., thinking about pushing for the divorce. I sincerely hope that you will take some time to think about this and do it w/a calm and clear head and not from a place of anger, disgust or from the pain it has caused you. However, whatever you decide to do, we will support you.