The Not So Little Merman by C.W. Gray

Kit Rees is one of the many children of the King of the Southern Silver Isles. Despite being a prince and third in line for the throne, he is too chubby, too loud, and too unsophisticated to truly fit in with the rest of the southern court. He lives a luxurious but lonely life, unnoticed in the castle and quietly wishing for the freedom to simply be himself.
Tack Muir is the crown prince of the infamous Northern Silver Isles. He has a reputation for being cold and pragmatic, but even the strongest merfolk have weaknesses. Tack’s happens to be a cute, red-headed merman from a rivaling kingdom. When an arranged marriage gives the two kingdoms a chance to form an alliance, Tack gets the chance to be with the one person he longs for most.
The problem is that Tack’s family curse ensures that he cannot touch any living being. Tack has learned to live with the curse, and he’s also learned the danger of hoping for more. Hope, however, is sneaky little bugger, and the more time Tack spends with Kit, the more he hopes for the impossible.
To find their own paths to happiness, the two men must break a centuries old curse. However, family enemies, old magic, and their own stubbornness just might stop them.