Does wife needing time and space always mean cheating?

My wife and I recently separated after 9 years. We have been separated for 2 months. She said she needed time and space after some major disagreements over our developmentally disabled daughter. It started with her saying it could go either way, but after two weeks she was saying never to counseling and was ready to file for legal separation. Admittedly, I did all the things you aren't supposed to do during the first month: beg and plead, send flowers and gifts, etc. She still hasn't filed for legal separation after two months. Everyone asks me if there is someone else. She has always been a high character person, but I do wonder now. Does needing time and space always mean there is someone else? I'd like to hear from women who were in a similar situation as my wife.