unfaithful
adjectiveUK /ʌnˈfeɪθfəl/
US /ʌnˈfeɪθfəl/
Not doing what you promised to do.
The dog was unfaithful and ran away from home.
OTHER MEANINGS
2. Not accurate or exact; not matching the original.
The movie was an unfaithful version of the book.
3. Having a romantic relationship with someone other than one's partner.
She discovered her husband had been unfaithful.
4. Not believing in or following a religion.
In some old stories, unfaithful people were punished.