Bad Day...again...

Today was not a good day.  I have been trying to control my anger, especially at work.  But sometimes it doesn't work.  See, there's a person I have to work with that really irritates me, not because they speak to me or do things directly to me, but I used to be friends with this certain individual and her choices in life really anger me.  My other half works at the same place I do, and if I happen to see her talk to him, my blood starts to immediately boil and I would love nothing better than to rip her apart.  I feel like she has NO RIGHT to speak to him because he is my other half.  But he has to be professional and it kills me.  She is very flirtatious and dresses inappropriately at times and that just puts me over the edge because I feel like she doesn't respect other people and crosses boundaries that shouldn't be crossed.  
My anger boils over because there really isn't anything I can do.  Violence is not the answer, but it certainly does cross my mind.  I'm tired of this venom running through my veins...how do I let go of my hatred toward this person?  I've been doing research, righting in my journal, trying to find an outlet, but some days I just can't seem to be logical about it, especially being so near this person 5 days a week...I know I need help.  I've never hated anyone in my life.  How do I overcome this before it destroys my relationship and my soul?