Criss Cross (movie, 1949)

Burt Lancaster plays Steve Thompson, a man who seals his dark fate when he returns to Los Angeles to find his ex-wife Anna Dundee (Yvonne DeCarlo) eager to rekindle their love against all better judgement. She encourages their affair but then quickly marries mobster Slim Dundee (Dan Duryea). To deflect suspicion of the affair, Steve Thompson leads Dundee into a daylight armored-truck robbery.