How do I stop myself falling in love with my best mate's wife who I am currently sleeping with but not behind his back?

you try to think negative about your mate's wife, so that way you can stop yourself falling in love with her. by thinking that she's not perfect for you, nor good looking or you can think she is out of your family background, your living style and you can get some other beautiful girl better than her in your future. GOOd LUCK!!!!!!!!!!!!!!!!!