There's a fine line between intimacy and invasion.
Closeness is desirable and yet terrifying. I'm sure you can think of an example from your own life where just when you were starting to get close to someone they panicked and backed off. If the wrong person tries to get close to you, don't you feel that panic and revulsion?
To me, this is one of the richest sources of story conflict imaginable. In "Cold Words" (Analog Oct. 2009), my character Rulii said about his friend Parker,
"I do not know to love or cringe, that a foreign creature can nudge me so close."
Another classic example of the same thing is the relationship between Genly Ai and Therem Harth rem ir Estraven in Ursula K. LeGuin's book The Left Hand of Darkness. Two individuals who are fundamentally incompatible for intimacy find themselves thrust into an intimate situation. The conflict - the tension - it's incredible! And it even demonstrates what I was saying about intimacy, invasion and retreat, because when the two attempt to speak through telepathy, Estraven discovers that Genly's mental voice sounds like the voice of his dead brother, and asks him not to try to speak to him that way again.
You could argue that the way that the "Ewu children" are treated in Nnedi Okorafor's new book Who Fears Death (DAW 2010) is related to this intimacy/invasion borderline. These children are born of unions - either willing or unwilling - between two races, one of which is trying to eliminate the other through genocide. The Ewu children, as evidence of intimacy between people who are "supposed" to be separate, engender extreme reactions of revulsion, disgust, contempt, and even violence.
If you've ever wondered about the draw of romance novels, I think it has a lot to do with the fascination of intimacy. Intimacy is the goal - revulsion and the fear of invasion are the risks. It's a conflict that speaks deeply to all of us, even though it's not necessarily always about love or sex. Rulii has lost the support of his family because of personal choices, and is desperately lonely, but afraid to pursue the brotherly intimacy he has begun to feel with the human linguist, Parker. There are opportunities too to play with intimacy/invasion conflict in the mentoring relationship that is so common in stories. Obi-wan acts like Luke's father, but who is his real father? And who does Luke get angry with when he finds out? Harry longs for his lost parents and wants to get closer to Dumbledore, but struggles when Dumbledore pushes him away for his own protection... Look also at all the buddy movies out there, and how the guys try to prove their worthiness to each other without getting too close. I'm sure there are many many more examples.
If you're writing a story, look around for possible intimacy/invasion conflicts. One might be at the center of your story, as with my novel in progress For Love, For Power. Or there might be a minor character in your story, perhaps a confidant or guide to the protagonist, who could take on additional dimension if you can explore the relationship and find where the intimacy/invasion borderline lies between them. It could be as simple as styles of politeness, where one group of people expresses alignment by honoring the autonomy of others, and another group expresses alignment by using expressions of intimacy with them (oh, the possibilities for offense!).
The borderline between intimacy and invasion is a powerful ally to any writer who wants to intensify conflict in a story and increase the engagement of readers.
It's something to think about.