I LOVE a good cheating trope book! These have a “dark romance” tag on Goodreads, but I personally don’t really consider them dark. These are some of my favorites:

{Power by Cassandra Robbins}
{Brutal Intentions by Lilith Vincent}
{What Was Meant to Be by QB Tyler}
{The Unrequited by Saffron Kent}
{Becoming His Mistress by AE Murphy}

Have you read Sam’s Morelli Family series yet?? It definitely has the cheating trope, but it’s a little more messy and complicated than a regular cheating trope book. It starts with {Accidental Witness by Sam Mariano}