Some people are just oblivious of their behaviors. They act like jerks and wonder why they have no friends, why people flee when they walk into a room. They do everything they can to stay “right” in their mind and end up pushing people away.
You cannot keep hurting someone and not damage the relationship you have with that person. Some people are resilient, some others are patient (borderline masochist), and others are just “used to it”. However, there is a limit to it. One day, the relationship will react to the strain and will end up irremediably broken because a relationship entails that the two people in it show some selflessness; the give-and-take in it has to go both ways.
Little can be done about it apart from using brutally direct means of raising these people’s level of awareness, and ever then, nothing guarantees the success of the “intervention”.
I think it is sad that crucial relationships end up strained and broken (and one person in it in pain) when the oblivious person doesn’t care enough—after being told—to make the necessary changes to preserve the relationship.