someone, usually a man, who cheats on his partner; a man who betrays, or is unfaithful to his wife or girlfriend.
Russian Folk - The Crescent's Been Colored With Crimson
"You can't? Well, is that so, my darling?
But long in the past now foregone,
Remember, the treacherous love rat,
How I trusted you to go on?"
Russian Folk - Along the Murom Tract Road
He saw my bitter tears and lowered eyes in shame,
The love rat realized that my life went up in flames.
What are idioms?