This seems to be hit or miss, entirely dependent on whether or not you have the 5's focus. When I am zeroed in on someone this tends to come easily and my naturally detached, analytical demeanor is going to seize upon body language, word choice, and anything I can determine from observing this person in order to figure out their motives and what they're trying to really say. If, however, you do not have my attention it's not like this awareness runs in the background. I believe that's why we can, at times, be incredibly oblivious.
With an SO or a close friend, if I notice a deviation from your usual pattern of behavior or interaction I'll look to body language to help me figure it out but I probably won't bring anything up and I'll just leave you alone. Pro-tip: pouting or being evasive for an extended period of time isn't going to make us come to you, but we're going to give you even more space with the perception that you'll figure things out on your own, since that's what we do. Which tends to be the opposite of what people want.