An insincere person should not be trusted
Hypocritical.
It can depending on the person and it also depends if you are the one being unfaithful/ insincere or if your spouse is.
Your countenance belies your insincere request.
An insincere apology is no better than no apology. I noticed that she was insincere when she said the shirt that was too small for me looked good.
The word 'glib' means fluent but insincere.
He made a show of caring and wanting to help, but we knew he was insincere.
lacking sincerity; "a charming but thoroughly insincere woman"; "their praise was extravagant and insincere
Irresistible, Insecure, Insincere, Idiotic, Immaculate, Immature, Immovable, Idyllic, Imperfect ...
yes
insincere
No.