What I'm dealing with, and I thought I made the term up but somebody beat me to it, is a foul-weather friend.
This is bad enough, I suppose. What makes it worse is that, every single time without fail, I forget who I'm dealing with. I think that things are better now, that the rough patch has smoothed out, bullshit like that.
I'm not stupid. Really, I'm not. I just seem to have blinders on in certain situations, when dealing with a certain person. Then reality once again knocks me upside the head, and I get angry at myself. Not for being a nice person when help is requested, but for expecting any sort of niceness, or even common courtesy, in return.