obsessive licking

Question
I have a male chihuahua and a female akita\american bulldog mix.  My chihuahua was calm, loving, and good natured until our female was brought home recently.  Now he won't sleep unless she is sleeping, he won't eat until she is done eating her food, and he doesn't listen to any of our commands anymore.  Worst of all, he won't stop licking her private area.  When I take them outside to potty, he will drink her pee after she goes.  Then he twitches and his teeth start chattering.  No matter what we do, he will not stop.  This does not seem normal.  What should we do?

Answer
If he isn't neutered, do so.  It is no cure all, but should be a big help in this case.  Spaying her may help too.  No reason to keep an intact mixed breed.  That is such radical behavior, if the spay/neutering doesn't help, you may need a private trainier.