Short of framing them separately, putting physical distance between two characters is one of the best ways to convey emotional distance.
Examples of distance
In the first episode of the BBC television series Luther, the antagonism between DCI John Luther (Idris Elba) and Alice Morgan (Ruth Wilson), is conveyed by their physical distance in the frame. During her interrogation, director Brian Kirk starts the scene with a medium shot, showing the two characters separated by the table in the interview room. Luther has his legs crossed and sits back slightly, only accentuating the space between the two characters. As the scene progresses, Kirk shows the two characters in close up, their faces at the extreme edges of the frame.
A similar technique is used in American Beauty, when director Sam Mendes conveys the emotional distance between Lester Burnham (Kevin Spacey) and his wife Carolyn (Annette Benning) by seating them at opposite ends of a long dinner table.
Want to convey an emotional breakdown between two characters? Need a visual way to convey their estrangement? Try using heaps of space between the characters in your shot.