This is Killian Coyle from a romantic suspense novel I wrote as Kiley Beckett.
It's a violent crime story hung up on the beats of a romance plot, where the intertwined male-female relationship is paramount, though the dangerous criminal world revolves around them.
The back story: Killian is a former SAS operator who heisted a bank in Marseilles with some of his other special forces friends, liberating over a hundred million in Jihadi-terrorist diamonds.
But in this book (Killian appears as a side character in the first "Dying for Diamonds" book, "Broken," featuring a different couple) Killian's come to a tiny Idaho town looking for the man who killed his brother. It involves fentanyl and arms deals and bikers and rodeos and has shootouts and hot dirty sex.
The female main character is named Ava Monroe, a down-on-her-luck hospital nurse who was unlucky enough to fall for an Irish temp nurse (Killian) who turns out to be yet another liar and con man. But when this betrayer winds up wounded and needing her medical help she can't refuse him...