I'm not sure where you saw that reference, but I do know that there has been a fair amount of research on nonverbal mirroring, which is typically called "mimicry" (that's the keyword I'd search for). Tanya Chartrand is one of the main researchers doing this work; here is her CV (pdf) which lists her published work (most of the relevant ones have "mimicry" in the title). Her 1999 paper with John Bargh (pdf) is probably the most prominent paper on the topic, and here (pdf) is a more recent paper which I picked because it's available for free & it starts with a decent summary of existing research on the topic.

The kind of thing that you're interested in - the development of thought/emotion/behavior patterns that span 2+ people in a relationship - is also an active topic of research. I don't know as much about this area, but I do know that Mischel & Shoda have created one model of it. Here is the abstract of one paper of theirs which seems particularly relevant but doesn't seem to be free online, and here (pdf) is another paper which is available for free.