An aper is a person who apes or imitates something or someone else.
When a person imitates another person, it is called mimicking or copying.
The term "copycat" likely originated from the behavior of cats, who are known for imitating movements and behaviors observed in other cats. Therefore, when a person imitates someone else, they are referred to as a "copycat" due to this mimicry of actions and behaviors.
Echopraxia is the sudden urge to imitate someone. So they might be Echopraxic?
If you are involved with a person you catch flirting with someone else, you can confront them about it.
It shows how a person explains the behavior of someone else.
Such a person is a bully.
A bewrayer is a person who betrays someone else, or who divulges information to someone else.
You should not date someone when they are with someone else because that means that the person you are with is cheating.
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imposter
An educator is someone who teaches or learns from someone else.