Jealousy

My boyfriend and I have been together for over a year. We have been in seperable since the day we met and madly in love. He is good looking, a very likeable character and is overly friendly with everyone which often comes across flirty. I have no problem with this as I know that's just his personality and that it does not vary on who he's talking to.
However. A number of so called friends have not only got feelings for him but have acted on them. They have gone out of their way to talk to I'm all the time (in front of me) and have told him they have feelings for him. There's not many people in our area so that's why I think people are so desperate. How do I stop the anger? Everytine I see these people I get so upset so jealous and so angry. I can't trust anybody it's so annoying. I've ignored the situation but have still somehow come out as the bad person. I don't know what to do anymore. I feel betrayed and like everyone is against me. I feel like a paranoid crazy person. How do I stop this from irritating me. 
How do I get over jealousy?