un-warranted jealousy

I have a jealousy issue. I am engaged and love my boyfriend. However if i find him talking and acting friendly towards another woman I freak out. I will shout and yell because I am immeadiately convinced he is cheating on me becauses she's so pretty, looks nothing like me and has got bigger boobs etc...etc... It is ridiculous because he has never cheated on me and I don't feel I have an issue in the past with someone cheating on me that I am bothered about,(and inevitably the girl has a boyfriend or Husband.) So where does this come from? Afterwards I can calm myself down and realise how stupid I am being but if someone mentions it I convince myself again, yell at him, and yet again have to calm down. This causes no amount of arguements as he has never (as far as I know) actually DONE anything. In an arguement I will do stupid things like threaten to jump out the window etc... He will just ignore me at this point or sit there telling me not to be stupid at which point I will inevitably say "you don't really care about/love me, as long as YOUR ALRIGHT YOU DON'T CARE!!" These arguments all the time is killing our relationship as he is convinced I don't trust him ( I do it's the women I don't trust!). He has given me one more chance. I have to let him go out with his friends alone to pubs and clubs and parties, I don't know if I can do this, it tears me up inside not knowing whats going on. I need to save my relationship. What can I do?