i have had anger issues also. i grew up with a father with anger issues. but please dont think i have answers. and i dont mean to come across as knowing all you've gone through, and what you've done. and i'm dont mean to contradict DB or any of the posters.
i think i would start, if you havent done this already, by calling your W and telling her basically what you've told us, and apologizing for yesterday. tell her you're not expecting her to forgive you but that you're sorry regardless, and you understand why she is leaving.
and this is not to get her back. but to be honest with yourself.
make no excuses, take responsibility and the consequences. but let her know.
after that, go back on Cymbalta, and talk to your doctor about changing the dosage. or finding another prescription. If it helped before, then do what works.
i would guess that if you have searched for the reason, but cannot find one, then maybe its time to assume its chemical. still your responsibility, but not entirely your fault.
but dont quit, keep doing the good things you're doing, and i wish you the best.
"In a ham and eggs breakfast, the hen is involved, but the pig is committed".