About a month ago now my wife asked me to go to her moms house to pick up a dresser that was in the garage. She said her mom wasn't home and that the key to the garage was in a dish on her moms dresser. Well I went over and didn't see her moms car cause it was in the garage and opened her bedroom door to find her masturbating with a toy. I froze for a second and turned around and walked out. All she said was "hey there". She came out a few min. later and gave me the key. and then she said "well what do you think of your mother in law?" I didn't know what to say I got the dresser and left and haven't told my wife. For some reason it really turned me on and I can't stop thinking about her and I masturbate to her all the time now. Do you think this will go away? why am I lusting after my mother in law?