The Temporary Wife: Luca and Valentina's Story (The Windsors, #2) by Catharina Maura

From the author of The Wrong Bride and Forever After All comes an angsty and steamy marriage of convenience romance featuring a billionaire boss and his secretary.

When Luca Windsor's secretary suddenly quits her job shortly after his family forces him into an unwanted engagement, he sets out to solve both problems.

... by secretly marrying his secretary, Valentina, instead.

The rules are simple:

1. Don't fall in love
2. Keep their marriage a secret at work
3. Share a bed every night

It was meant to be a straightforward and mutually beneficial deal, but with each day that passes, it becomes clearer to Luca that the one thing Valentina wants is the only thing he can never do:

Letting her go.