Obsessive thoughts

How can I stop obsessive thoughts and desires. I'm not talking about thing usually associated with OCD, but constantly harboring harmful thoughts about someone I love

You can't reason with them and you avoiding things won't work either.
Well, for starters you should go see a professional psychologist because while there are things you can do for yourself, they will structure your efforts so they will work for you even more efficiently.

There are a few things you could try. Part of the answer lays in very persistently and repeatedly ignoring the thought in order to rob it of it's power and to desensitize yourself. By ignoring is meant that next time it is making you anxious and you want to try and reason it away or neutralize it, let it come to you instead. Some people said this made them literally get bored by their thoughts. A technique is to actually write the obsessions down, so maybe you can see them for what they are. So much easier said than done, I know... But no 1 ever said this would be easy but this is part of the real key to regaining some of your freedom.
Don't forget, this is an Anxiety Disorder, nothing will be really simple, every step you take to fight the OCD will be a direct confrontation with your anxiety. I force myself to think of the scary thought. And then avoid the rumination (for you, you probably try to prove to yourself in your mind that you would never do it, am I right? If so then that's your compulsion or rumination rather) This is what you need to avoid. At first this causes severe anxiety so you must be strong to do this. Does this make sense to you? Try it and let me know how it worked out. After a while the anxiety should subside and and the thoughts will still come but they will be like any other thought they will just pass. And watch out because your mind will try and find something else that will bother and scare you and you just need to recognize these thoughts as they come. The more you monitor your thoughts the more you will be able to distinguish the intrusive thoughts from the regular thoughts. Hope this helps you.
Take care.

Thanks, what really triggered this was yesterday when a co-worker had issues with this person and it just sent me on a tear that kept me up all night.

There are so many triggers. You might want to use those triggers to force the thoughts on. What do think in your head when you have the thought?

I have had thoughts about harming a loved one and it can be very disturbing. But I used the method that I just told you about and over time they wouldn't cause any anxiety. I would just recognize it as a thought and move on. You know that you would never hurt your loved ones. It's just the thought that is scareing you. It sounds like you have pure "o" ocd. Have you been diagnosed?