How to deal with this at work?!?

Guy I work with is on long term sick for a mental illness, he will be coming back I think. Anyway, for ages before he was signed off/diagnosed etc.. he would rub himself on me if I was bent over doing something and didn't know he was there, try and "accidently" grab my hand and nearly put it on his crotch, him putting it there, not me. Once accidently rubbing past my really, really slowly on purpose.He would always be talking about killing people, etc.. What should I do if he starts again after coming back?? I'm hoping the time off and proper esments/medicines etc may help. My boss knows that he used to do this before she started but she gets the impression that it stopped, she thinks I'm quite weak and not ertive enough (true!) so i couldn't tell her he still sometimes did it coz I know that she will get pissy with me for not standing up to him, but it can be embaring to say stuff. When I asked him not to do it once he just said that I wan't it really and that all men love a slag!! Which I'm not!! I just wear jeans, t-shirts to work so I am not leading him on by any means. My boss fancies him, or so I think and anytime I even mention this guys name she gets really defensive and aggressive and in a MAJOR piss for days with me. Any help??!! Thanks xxxxx