I thought the depression rumor was debunked? Somebody correct me if I'm wrong, but didn't Robin get a dementia diagnosis, and thus chose to go out on his own terms, rather than slowly rot away?
Half right - he did battle depression his entire life, and he was diagnosed with Lewy Body Dementia and Parkinson's not too long before committing suicide. There's really no way to prove which one influenced his decision more, but it was likely because of both.
It was Lewy Body Dementia. He had periods of lucidity and in one of those decided that he no longer wanted to live as a prisoner in his own body, and a burden to his family because for all intents and purposes his life as a functioning human was over.
Honestly his entire circumstance is a shining example of why we need a death with dignity law.