Sometimes you gotta be the selfish one, in order to ensure your emotional survival. Like I said.. I've been put in positions like this before, shouldering the burdens of others originally because I cared and wanted to help out, only to find them piling more and more shit on top of me until I had to just throw it all off because I was bordering on a nervous breakdown. But it had to be done, otherwise I would have killed myself. So I decided that, since killing myself would have the same effect (making them handle their own shit) that would happen if I threw them off of my shoulders, I just dumped them on their asses and told them they'd have to stand for themselves. And holy shit did they shriek and wail and f*cking HATE me for it.Eventually I just stopped hanging around these people because they wouldn't stop.
This may sound like the nuclear option, but... look for another job. I know that's an asshole thing to say, because jobs are hard to come by. But start in on your resume, get your things in order. If they are looking for you to be the dept chair, then clearly you have skills that could be appreciated elsewhere. They don't just hand out positions like that to anybody, right? You've got more power here than you realize.
Seriously, work on a resume.. It'll help you quantify what skills you have and your value as an employee (even if other assholes only value you as a shield). There are guides on Lifehacker and other sites which help you in putting those together. Then once you have a good one together, start quietly looking for other positions. With skills like yours you might find that you're more in demand than you thought you were. And if you find another one, then you've got choices, and -that- will make you feel like a million bucks.
If nothing else, doing a resume will make you feel better and help you realize all the skills and professional value that you are taking for granted. The process of doing mine certainly made me feel good.
:hug: