You don't! The only person one has complete control over is his or herself. Your power as an individual comes from "selecting" the kind of mate you want in life. It takes more time to truly get to know someone than most people are willing to invest these days.
The main thing you want is a person who values HONESTY above all else in relationship dealings. Cheating is all about lying (directly or by omission) and betrayal.
Remember "the same thing it took to get your baby is the same thing it's going to take to keep them". Never stop making your mate feel sexually desired. Too many people buy into the "do whatever it takes" to "win someones love" and then they revert back to their "natural self". If one started off being their "authentic self" they know their mate fell in love with them for who they really are.
Starting off flirting, using sexual innuendo, and various other romantic gestures only to STOP after he or she has become emotionally invested can cause problems. "When we change our circumstances change."
A cheater seeks to hold onto what is good in their primary relationship while seeking to fill the gaps with other people on the side. Strive to find out what your mate wants and if you can't or don't want to give it then they are not the person for you.