Renee Ryan 
Marshal Takes a Bride [EPUB ebook] 

U.S. Marshal Trey Scott is fixin’ to walk down the aisle just as soon as his stubborn bride-to-be agrees to say "I do." Katherine Taylor’s five-year-old sister and an orphanage full of children are depending on her. So why won’t the pretty schoolteacher marry him to save her tarnished reputation? Granted, Trey isn’t willing to abandon his quest to avenge his first wife’s murder. His name alone will protect Katherine until he returns, but she thinks he should leave vengeance to a higher power. Will the sacrifice demanded by the woman he loves be too great to bear…or will it be Trey’s ultimate redemption?