[archevel]

> People don't suddenly become less obnoxious, more mature, less possessive, just because there's someone else around.

In my experience the opposite is true people DO become more mature in the presence of others. In general people tend to take a breath and try not to lose face by becoming upset in most social contexts. Also a third party can mediate conflicts, couples therapy comes to mind. Sure that's not the same thing as romantic involvment, but I can imagine conflicts deescalating just by having a third person around who can see both sides or take side or point out that the arguing parties are both behaving as idiots.