How do i end it with my current partner?

How do i tell my wife im leaving her because i cant take the stress anymore? We have been going down hill for the past three months. I cant explain how many times ive came home late from the gym to be interrogated about who i was with or how every time we have she wants me to do things im not comfortable with.She has been trying to get me to roll play for the past year and when i finally agreed she wanted us to switch positions to as she put it see how its like for the other person. She also has a strap on vibrator she puts on when we roll play. She puts me down in front of our friends and family and the other night i came across a picture of a man in the email she left up....HELP ME