So you've stepped back, enlisted help and confronted the person making your life difficult and nothing has changed. What do you do next?
If it's a work situation you may need to enlist your boss's help. Be sure to address the issue as one of productivity affecting work issues and not as a personal one.
Whether or not this is work-related there may come a point where you have to simply leave the ring. You're probably thinking "But why should I be the one to leave? I'm not the one causing the problem!"
That may be true, but what price are you paying in terms of your health, success and happiness? On-going stress affects everything else in your life. Do you really want to be held hostage to someone else's problem?
Only you can decide if the good in your current situation outweighs the bad. If you decide it does, then redirect your focus to the good and stop giving the other your attention. If you choose to leave then put all your energy into that immediately.
Positive action is always your best defense.