Double affair
When someone cheats on their boyfriend / girlfriend / fiancé / fiancée / husband / wife with someone who is also in a relationship or married.
Hanna: my ex had a double affair, he cheated on me with his cousin’s fiancée.
Kate: maybe if you would’ve given him head, he wouldn’t have cheated on you.
Kate: maybe if you would’ve given him head, he wouldn’t have cheated on you.