Computer-HARD should be embarrassed! (KIA)

Ok.  The computer was killing me.  I made a couple of bad decisions, and was heavily paying the price for it.  And then suddenly, out of the blue, the computer sacs a rook.  And then proceeds to lose.  I think I know why - I actually got it into a perpetual situation, and it had been winning the entire game, and refused to draw with me.  So it lost instead!  That's my theory, anyway.  See what you think.

Annotation by Fritz, who curiously doesn't call out the losing move by black.  I guess computers have to stick together!