hahahahahaha...Here we also learn how to be a betrayer heheh.... Sorry, I just couldnt help it! Twas the first thing that came up in my mind when I listened to that woman!!
you can say "trapaceiro/traidor". Cheat = trapacear. But,if it is on a test at school you say "colar". Betrayer = traidor; deceitful = enganador/ falso. But, if it is another person in a relationship (like a marriage) use "o/a amante"