adulterer

noun4

1. •
   One who commits adultery.
2. •
   A spouse who has sex with a non-spouse.
3. •
   Someone who cheats on their spouse or monogamous significant other.
4. •
   A male adulterer specifically.

   • I become an adulterer and remain an adulterer when, by choice, I freely adopt the proposal to have sex with someone other than my wife. — 2005