my two cents on this.
whenever you interact with someone else, your going to get emotionally involved, to some degree, its human nature.
even when your roleplaying, and by that i mean, places like tombstone, fantasy sims, crack den, midian .. your still getting heavily involved emotionally everytime you play a scene.
The more time you spend with someone, the more you tune into their feelings. I've had some friends who i've known from day 1 in
SL and i know when their feeling down even through the way they talk/type, and so i'll do my best to make them happy, or let them talk about it.