Cool project; interesting to try to visualize something like a personal relationship. It's not clear, though, if the "transit time" -- the period between when the message is sent and when it is read -- of the message is accounted for; that is, all the message "comets" seem to move at the same speed, and in many cases the recipient appears to fire off a new message before the incoming message has even arrived.

Maybe there are some external circumstances that frequently caused both users to simultaneously message one another, but I would have expected to see more of a clear back-and-forth pattern where each message provokes the following response.