Were you on leave for medical reasons? I'm not sure where you are, but if you are in the US, then his response to your absence was illegal. If you destabilize because of his harassment, he can be held legally liable. You have rights and he is violating them. I know how unhelpful HR departments can be - been there, done that. I ultimately left that job and it was the best decision I could have ever made. I know, at least in the US, the economy is pretty bad right now, but I would still start looking for another job, just for your own peace of mind. You may also want to consult a lawyer - they usually can give free consults - just to see what the extent of your rights are and what, if anything, can be done. Don't let him overpower you.