All I Do by Tamara Lush

Remy Hastings is known as the playboy of Paradise Beach, and he can’t believe his luck when a gorgeous mermaid literally swims up to his boat. She’s not a real mermaid, of course, but a woman with a gorgeous… tail.
Leilani Kostas is opening Mermosa, a mermaid-themed bar on Paradise Beach. When she finds Remy Hastings in the Gulf of Mexico, she’s intrigued by the bronze-skinned, amber-eyed boat captain. But even though she’s always had questionable taste in men, she’s a bit mer-mazed when she follows him back to his sailboat for a hot night of fun.
Before they hook up, Remy lays down the law: no-strings sex. He’s a confirmed bachelor. Leilani enthusiastically agrees, because she’s getting out of a bad relationship.
But for the first time, Remy wants more than one night. Soon, no strings turns into a tangled knot, and for the first time ever, Remy’s casting a net for only one woman…