“Someone who smiles too much with you can sometime frown too much with you at your back.” 
― Michael Bassey Johnson

Deception, beguilement, deceit, bluff, mystification and subterfuge is the act of propagating beliefs in things that are not true, or not the whole truth (as in half-truths oromission). Deception can involve dissimulation, propaganda, and sleight of hand, as well as distraction, camouflage, or concealment. There is also self-deception, as in bad faith.

Deception is a major relational transgression that often leads to feelings of betrayal and distrust between relational partners. Deception violates relational rules and is considered to be a negative violation of expectations. Most people expect friends, relational partners, and even strangers to be truthful most of the time. If people expected most conversations to be untruthful, talking and communicating with others would require distraction and misdirection to acquire reliable information. A significant amount of deception occurs between romanticand relational partners.[1]

Deceit and dishonesty can also form grounds for civil litigation in tort, or contract law (where it is known as misrepresentation or fraudulent misrepresentation if deliberate), or give rise to criminal prosecution for fraud.

https://en.wikipedia.org/wiki/Deception