In the question of interpersonal relationships, many people who are considered nice are actually very, very vile indeed.
It is those individuals who have nasty dispositions at their core who are skilled in crafting the polite, responsible image for casual aquaintances to see, though in private, they abuse, neglect, and use their closest friends and family. Because they are so adept at making aquaintances believe they're extremely good people, the close friend has no choice but to fall into the role of used and never break out, hense the entire circle of friends or family discard that individual, and question how he could be so obstinate to someone so reasonable and responsible. These "nice" people are the parasites of every group, and every group has one.
It is because people are so stupid, so easilly suckered by the behaviour of these insidious parasites, that they will never see true fault, or percieve the true instigator of any conflict. They only see the surface, the image the parasite has done so well to craft. They don't deal with that person on a more personal level, so they have no conception that anything but what they see could be true. They blame the person with the less well-crafted image, surely he must be at fault; after all the story told by the more Charismatic individual sounds so plausible and right, it must be the truth.
Just remember, if one person is constantly complaining of how much they do for others, they really do nothing, for everything they do, if anything at all, is for them, so that they can later use it to get something of greater value in return out of obligation and friendship.
I don't have any friends personally, but it isn't hard for the thinking individual to see this going on.