unfaithfully

adjective

1. failing to observe the terms of a vow, promise, understanding, etc., or false to allegiance or duty; faithless; disloyal
2. not true, accurate, or reliable; untrustworthy
3. engaging in sexual relations with someone other than one's spouse, lover, etc.; adulterous
4. Archaic lacking good faith; dishonest
5. Obsolete infidel