The Right to Surrender by HM Thomas

Bad boy Finn James and rich-girl-turned-undercover-agent Gretchen Christensen have known each other their entire lives, but when Gretchen is sent to infiltrate the shady world Finn inhabits, they’ll have to depend on each other to keep their secrets.
Gretchen has been in love with her older brother’s friend for years, but Finn doesn’t think he’s capable or worthy of love. When she comes back into his life, he can’t deny his attraction to her or his desire to protect her. As his interest in her gains dangerous attention from his supposed allies, he’s forced to surrender to his feelings and decide which version of his life he is willing to live permanently.