(guilty) of adultery

unfaithful

(an instance of) voluntary sexual intercourse of a married person with a person to whom he or she is not married

extramarital affair

the act of causing a person to accept as true or genuine something that is false

practice of misleading

not honest

lying, untruthful

not loyal (to a person, one's country etc)

unfaithful

outside the regular course of academic work or studies

unfaithful

disloyal

disloyal

(of a person) often changing one's feelings about another person

vacillating, blowing hot and cold

something imposed, e.g. a tax, burden, fine

deception

(an act of) disloyalty or being unfaithful, especially to a wife or husband

disloyalty to an obligation

(the act of, an instance of) stealing

stealing

deception, joke

deception, joke

not ethical

dishonest, immoral

not fair or just

prejudiced, wrongful

not true (to one's duty, a promise etc); committing adultery

disloyal, adulterous

without moral principles; dishonest

corrupt

not fair; not sporting

prejudiced, wrongful

false; disloyal

dishonest

tricks used to get something one wants

cunning