Sworn to Revenge (Sworn #2) by Dor Friedman:
 
"She can lack morals, she can lack control, she can lack fucking common sense for all I care, but she’ll always have me!"

Bay

My world is drowning in lies and betrayals I can’t escape. My family’s sins chase me. Revenge is the only anchor I have left. Yet every step back to Pedro feels like losing myself all over again—because when he looks at me, I start to wonder if revenge is worth it.

Pedro

She's a whirlpool I can’t contain, a mess of secrets and scars that I want to shield—even from herself. But keeping Bay close is a gamble; my brother’s orders tie my hands, and I’m forced to watch from the sidelines. She’s marked by blood and danger, but I can’t walk away. Not when she’s mine, whether she wants me or not.

Book 2 in the Sworn Series, keeping the unique blend of magic, mermaids, and mafia romance in a world where blood binds, betrayal cuts deeper, and the ocean hides more than secrets—some fates are sworn, and others are claimed.