Claimed By the Outlaw by Cyndi Faria

Emily Lyffe doesn’t believe in everlasting love, so when she receives a text from her ex-fiancé reminding her she agreed to meet him in Deadwood, she’s ready to set him straight.
Little does Emily realize, the summons originated from the ghost of Outlaw Wild Bill Hickok, who’s convinced she’s his reincarnated wife—and he’s dead set on claiming his bride.