Under the Gun by Cari Z

Life is plenty exciting for Joey Cole. Everything that isn’t his day job revolves around having fun, but “fun” becomes complicated when Joey’s latest side gig turns into a gunfight between the handsy billionaire he’s working for and the ex-boyfriend who broke his heart and who’s now…smuggling drugs?
Turns out that Adam, Joey’s ex, is a spy for His Majesty’s government, and that Joey has fallen into a sting operation meant to take his shady employer down. Joey and Adam are hounded by assassins as they escape to a safe house in England, home to the woman who introduced Joey to Adam in the first place—his grandmother.
Who, it turns out, is also a spy. Huh, no wonder she made him get so good at untying knots with his hands tied behind his back.
Joey and Adam rekindle the romance that burned between them, but Adam is still a spy—he’s not his own man, and he’ll certainly never belong to Joey. The safest thing would be to break it off before Adam breaks his heart again…but the way they’re being hunted, safe is out of the question, and love may mean the difference between life and death.