Too Much Jealousy!!!

I love my boyfriend more than anything in this world, and i want him to enjoy life to the full etc, but i get insanley jealous over anything that has him in contact with another woman. He gets on with a lot of people and is quite often in contact with loads of different people. But i can't seem to get over the fact he goets on with so many women! He has a particular friend who flirts with him all the time, and always touching him, and sometimes makes me feel quite ill, as i get so jealous. I know this all stems from early on in our relationshio, he called it off for a while and went out with another girl whom he'd started to 'fall' for when he was still with me. Then, about a month later, he asked me back and was a complete wreck. Turned out that he was given death threats to split up with me by some people i used to know. But he admited to this girl that he loved her and would never leaved her. He said that he thought that he could feel the same love for her as he did for me and turned out he couldn't. We are happy and love each other very much and i know he'll be faithful, but jealousy....It makes me ill sometimes. I have an absoloutly wonderful friend, who has been the ONLY person to put my mind at ease when i've expressed concern, and i love her dearly. But the jealousy comes back whenever he talks about or to other women. How can i get over this?? Help!!!!!!