About The Same Time My Wife Sterting Menipausing I Noticed

About the same time my wife sterting menipausing i noticed she started masterbating in bed at night while my back was turned, when i turned towerd her she,d stop. I confronted her about it and she said i imagining it. This goes on every night. I,ved moved out and am afraid to go back, she wont stop and she wont admit. What is causing her to do this?