noun
cheater; unfaithful person; adulterer
Refers to a person who is unfaithful in a romantic relationship; can be used for either gender, though often for men. Slightly colloquial.
彼は浮気者だから、彼女に振られた。
He's a cheater, so his girlfriend dumped him.
浮気者は信用できない。
You can't trust a cheater.