Yes, I am often very busy... part of my distress is I know I have probably been too hard on this particular person, and am beating myself up over it, for no really good reason. This is the same friend who tells me I worry too much. :-) This too shall pass.

Is it possible all three of you could have a conversation? Granted, it would be most uncomfortable, but it might work. Then maybe you could find out why X has acted in such a way, and then act accordingly. Your idea that perhaps this person is miserable, and wants to make everyone else miserable, may be right.