what is the correct to write
the reality between which he is torn sympathizing and vilifying
the reality which he is torn between sympathizing and vilifying
I don't think so. I have a vague sense of what you're getting it, but it reads awkwardly. First of all, "between" implies at least two alternatives, but you're using in conjunction with the singular word "reality". I'd at least make that "realities". Even your second stab at it strikes me as missing something. The sentence is really confusing. If "reality" is your subject, I don't think you can either "sympathize a reality" or "vilify a reality". If you're talking about the reality of "his" condition, I think it really needs a rephrasing... something like, for instance, "The reality was, he was torn between sympathizing [with person X] or vilifying [person X]." I confess, though, I might be off-base with just what it is you're trying to get across. To be honest, I think you'd have to give us a fuller context than you have to get a decent answer.